The best current open-source PLC software for a conventional IEC 61131-3 project is usually OpenPLC v4 or Beremiz. OpenPLC gives learners and builders a modern editor plus a separate runtime and direct board targets. Beremiz gives engineers a mature standards-oriented IDE, build toolchain, runtimes and optional integrations. matiec is an IEC-to-C compiler component, not a complete PLC package. Eclipse 4diac is a strong open-source option for distributed IEC 61499 function-block systems, but it is not an interchangeable IEC 61131-3 ladder environment. ProviewR is a broader Linux process-control/soft-PLC/HMI system. ClassicLadder is a useful historical ladder/Grafcet project, not the default for a new supported machine.
That answer is more useful than calling everything “free PLC software.” An editor, compiler, runtime, I/O layer and maintainable deployment are separate responsibilities. A tool can be open-source and still be a poor fit for your controller, operating system, real-time target, fieldbus, security policy, license obligations or support horizon.
This guide was technically reviewed on August 30, 2026. At that review point, the official repositories identify OpenPLC Editor v4.2.11 and Runtime v4.1.10; Beremiz documentation identifies the current 1.5.1 documentation surface; Eclipse lists 4diac 3.2 as its latest release; and ProviewR publishes V7.0 documentation. Always recheck the official release, license and security records before you install or deploy.
Open-source PLC software shortlist
| Tool | What it actually is | Standard/model | Best fit | Main qualification |
|---|---|---|---|---|
| OpenPLC Editor + Runtime v4 | desktop/web editor, compiler pipeline, board targets and headless runtime | IEC 61131-3-oriented LD/FBD/ST and related language surface | learning, research, embedded targets and soft-PLC prototypes | Editor, runtime and board deployment are distinct paths; verify current feature and license scope |
| Beremiz | IDE, PLCopen-based project model, compiler toolchain, Python/C++ runtimes and extensions | IEC 61131-3 | engineers who want a transparent configurable toolchain | installation and target integration require more engineering than a packaged vendor PLC |
| matiec | IEC 61131-3-to-C compiler project | IEC 61131-3 compiler | researchers, tool builders and Beremiz-style build pipelines | not an IDE, runtime, I/O layer or complete control system |
| Eclipse 4diac IDE + FORTE | distributed function-block IDE, build tooling and portable runtime | IEC 61499 | event-driven distributed automation and research | execution and application model differ materially from IEC 61131-3 PLC scan assumptions |
| ProviewR | integrated Linux process-control system with PLC, HMI/SCADA, I/O and communications | its documented graphical PLC/process model | Linux soft-PLC and process-control systems needing an integrated stack | not a drop-in vendor PLC or a simple cross-platform teaching editor |
| ClassicLadder | lightweight ladder and sequential/Grafcet project | ladder/sequential control | maintaining existing niche integrations or studying a compact ladder engine | older, narrower project surface and support model; assess activity and target fit carefully |
“Open source” describes source availability and license rights. It does not mean every feature is gratis, every compiled application has no obligations, every deployment is supported, or every project is suitable for safety-related control. Read each component's exact license; do not apply the editor's license summary to the runtime, libraries, generated program and third-party drivers as if they were one work.
What a complete open-source PLC stack needs
A usable PLC system needs at least seven layers:
- an editor for Programs, Functions, Function Blocks, variables and configuration;
- a compiler or code generator that implements the chosen language semantics;
- a scheduler/runtime that executes logic predictably;
- an I/O abstraction that maps program variables to physical or network data;
- build, transfer, monitoring, trace and diagnostic tools;
- a versioned backup, update and rollback process; and
- hardware, operating-system and cybersecurity controls appropriate to the consequence of failure.
An open-source ladder editor that draws a correct rung satisfies only part of layer one. A compiler that emits valid C satisfies part of layer two. A Linux process scheduled with elevated priority can improve timing, but it does not by itself prove worst-case latency, I/O update time, power-loss behavior or suitability for a machine risk-reduction function.
Editor, compiler and runtime are different
| Component | Input | Output | It does not prove |
|---|---|---|---|
| editor | user logic and project metadata | source/project model | generated code, target timing or field response |
| compiler | source and libraries | C/C++/binary/package | correct scheduling, I/O wiring or restart behavior |
| runtime | compiled program and configuration | repeated scan/event execution | electrical integrity or safe final-element action |
| I/O driver/plugin | runtime values and hardware/protocol calls | field data/commands | semantic correctness of the control requirement |
| HMI/monitor | runtime status and commands | displayed state and operator actions | source ownership or physical state unless independently validated |
Keep those boundaries visible during selection. “It supports ladder” does not answer which runtime executes it. “It supports Modbus” does not answer master/client versus server/device roles, data mapping, quality, timeout or stale-data behavior.
OpenPLC v4: the easiest current all-round starting point
OpenPLC v4 is no longer accurately described as the old Beremiz/matiec bundle. The current OpenPLC Editor is a GPL-3.0 desktop application built for Windows, macOS and Linux release targets. Autonomy Edge also documents a browser editor path. The separate Runtime v4 repository describes a headless runtime controlled by the editor through an HTTPS API, with a C/C++ runtime core, WebSocket debug, plugins and packaged deployment.
Current Runtime v4 documentation describes the STruC++ pipeline: the editor compiles Structured Text-oriented project content into C++17 sources, packages a program archive, uploads it to the runtime, and the runtime builds and loads a shared library. The previous matiec relationship remains important history and is still relevant to Beremiz and older OpenPLC generations, but it should not be presented as the current v4 architecture.
OpenPLC v4 component record
| Component | Current official description | Selection consequence |
|---|---|---|
| desktop editor | OpenPLC IDE with releases built for Windows, macOS and Linux | suitable for local project work; use the release repository as version authority |
| web editor | editor surface within Autonomy Edge with browser simulation/deployment workflows | account/cloud path differs from self-hosted open-source deployment |
| STruC++ | GPL-3.0-or-later ST-to-C++17 compiler with runtime-library exception and unit-test/REPL documentation | current compiler claims and coverage must be checked against its published compliance matrix |
| Runtime v4 | headless service/core controlled through HTTPS, with debug and plugin layers | not the old v3 web portal; secure and operate the API/runtime host |
| board targets | desktop documentation lists Arduino-style and industrial board targets plus Runtime v3/v4 targets | direct USB/board deployment and network-runtime deployment use different build paths |
| Docker | official multi-architecture Runtime v4 container path is documented | containerization does not guarantee hard real-time or correct host I/O access |
Where OpenPLC fits
OpenPLC is the strongest first choice when the goal is to learn LD/ST/FBD concepts, run a bounded soft-PLC lab, target a supported low-cost board, inspect a real open toolchain, or prototype a non-safety function whose failure is controlled. Its public repositories and current release cadence make it easier to inspect changes than a closed vendor IDE.
Do not convert that recommendation into “use it for any production machine.” A production decision still needs a hardware environmental record, I/O electrical design, measured scheduling/latency, watchdog and restart tests, secure configuration, update/rollback plan, spare/replace strategy, validation evidence and a separate safety architecture where risk requires one.
Beremiz and matiec: a transparent IEC 61131-3 toolchain
Beremiz is a complete Free Software machine-automation environment, not merely an editor OpenPLC once borrowed. Its current documentation describes a PLCopen TC6-based project/editor model, project POUs, resources, tasks and instances; a build toolchain; Python and C++ runtimes; online transfer/trace/force functions; and optional HMI, fieldbus and platform-specific I/O extensions.
matiec is one compiler within that broader ecosystem. Its repository is an IEC 61131-3 compiler codebase licensed under GPL-3.0. It can translate supported IEC source to C, but it does not provide the whole IDE, target scheduler, I/O drivers, transfer security, HMI or maintenance lifecycle.
Choose Beremiz when
- a standards-oriented IEC 61131-3 project model matters;
- you want to inspect and adapt the build/runtime path;
- Python or smaller C++ runtime options fit the target;
- Modbus, CANfestival/CANopen, BACnet, HMI or custom extensions match the documented path; and
- the team can own Linux/build dependencies, deployment and long-term integration.
Beremiz's repository documents separate licenses for the IDE, Python runtime and C++ runtime. Treat that as a reminder to inventory components, not as legal advice. Review the license text for the actual version and distribution model. If you modify a runtime, link proprietary modules or distribute an appliance, get qualified license guidance for that exact architecture.
Eclipse 4diac is IEC 61499, not just another ladder editor
Eclipse 4diac is an active open-source environment for distributed industrial automation using IEC 61499. Its IDE develops function-block applications that can be distributed across devices; FORTE is the portable C++ runtime; and the documentation covers events, deployment, monitoring, communications and I/O integrations. Eclipse lists 4diac 3.2 as the latest release at this review date and publishes the components under EPL 2.0.
That makes 4diac a serious option for distributed/event-driven automation research and supported architectures. It does not make IEC 61499 an interchangeable dialect of an IEC 61131-3 cyclic PLC. A Function Block in each standard can have different execution assumptions, event/data coupling and deployment behavior.
| Requirement | IEC 61131-3 tool such as OpenPLC/Beremiz | IEC 61499 tool such as 4diac |
|---|---|---|
| familiar PLC language practice | direct fit for LD/FBD/ST/SFC-oriented work | not the simplest route for a traditional ladder learner |
| single-controller cyclic machine | natural mental model | possible, but distributed/event model adds concepts |
| distribute logic across devices | requires platform-specific tasks/comms architecture | core application/deployment model |
| event/data coupling | encoded inside PLC program and communications | explicit event-driven function-block network |
| portability claim | source still depends on tool/runtime extensions | deployment still depends on runtime/device profiles |
ProviewR and ClassicLadder fill narrower roles
ProviewR for integrated Linux process control
ProviewR describes itself as an open-source process-control system built around a Linux soft-PLC. Its V7.0 documentation covers graphical PLC programming, process graphics/HMI, distributed nodes, I/O, alarms, history and communications. It is closer to an integrated PLC/SCADA/process-control platform than a small portable IEC editor.
Choose it when the project needs a Linux-hosted control and operator stack and the team is prepared to own the platform. Do not choose it merely because you want one beginner ladder exercise; OpenPLC or a browser simulator has a smaller learning surface for that task.
ClassicLadder for existing or compact ladder integrations
ClassicLadder is a free ladder and sequential/Grafcet engine with historical LinuxCNC and embedded interest. The commonly referenced repository documents an older 0.9.113/2020 lineage. That does not make it useless, but it changes the risk question: a new production project should assess maintenance activity, compiler/toolchain compatibility, security, hardware integration and who will support the fork throughout the asset life.
| Question | ProviewR | ClassicLadder |
|---|---|---|
| primary scope | full Linux process-control system | compact ladder/sequential engine |
| HMI/SCADA | integrated documented surface | not the main value proposition |
| best use | process stations, operator systems and custom Linux control | legacy/niche ladder integration or study |
| adoption cost | larger architecture and operational ownership | narrower features and lifecycle evidence |
License, cost and “free” are four different questions
Open-source software can remove a purchase price while adding integration, validation and support work. Separate these questions:
- Can you download and study the source?
- Can your organization modify and redistribute the software?
- What obligations apply to the editor, runtime, libraries, plugins and generated application?
- Who pays for engineering, hardware, support, cybersecurity response, validation and ten-year maintenance?
License and lifecycle snapshot
| Project/component | Published license signal | Operational reading |
|---|---|---|
| OpenPLC Editor v4 | GPL-3.0 in official repository | inspect exact distribution/modification obligations |
| STruC++ compiler | GPL-3.0-or-later; repository documents a runtime-library exception | generated-program terms need exact version review |
| OpenPLC Runtime v4 | repository directs users to its LICENSE; driver docs describe same-project GPL terms | verify release license and every bundled/plugin dependency |
| Beremiz IDE | GPLv2 or later per project repository | IDE license is not the only license in a deployed stack |
| Beremiz Python runtime | LGPLv2 or later per repository | architecture/linking/distribution details matter |
| Beremiz C++ runtime | GPLv3 or later per repository | review appliance and proprietary-module design |
| matiec | GPL-3.0 repository | compiler source license does not make it a complete runtime license answer |
| Eclipse 4diac components | EPL 2.0 | inventory IDE, FORTE, libraries and deployed changes |
| ProviewR | GNU GPL with project-specific documentation/exceptions | read the actual version and generated PLC module terms |
| ClassicLadder | repository states LGPLv3, with an EMC-use note | treat older forks and bundled copies separately |
This table is engineering triage, not legal advice. Preserve each dependency's license, notices, source offer requirements and build record with the release. “No license key” is not a license analysis.
Total-cost worksheet
| Cost surface | Learning lab | Production control |
|---|---|---|
| software purchase | often zero | often zero for OSS core |
| engineering integration | low to moderate | potentially dominant cost |
| industrial I/O/enclosure/power | optional/small | required and environment-rated |
| test/validation | educational cases | formal requirements, fault and regression evidence |
| security/update | local clean workstation | asset inventory, patch response, segmentation and rollback |
| support | community/self-help | named internal owner or paid service agreement |
| downtime/spares | low consequence | business-dependent and often larger than software cost |
| safety/regulatory | keep outputs isolated | separate approved lifecycle and certified components where required |
Run a 30-minute proof-of-fit before selecting a tool
Do not compare websites alone. Give each serious tool the same bounded program and evidence requirements. The lab below is deliberately small but exposes editor, compiler, runtime, state, timing, monitoring and restart behavior.
I/O contract
| Variable | Type | Direction | TRUE means |
|---|---|---|---|
| StartPB | BOOL | input | momentary start request exists |
| StopHealthy | BOOL | input | standard stop circuit permits run |
| PartSensor | BOOL | input | part is present at inspection point |
| MotorFeedback | BOOL | input | approved motor/contactor running feedback exists |
| MotorRunCmd | BOOL | output | standard controller requests conveyor run |
| RejectCmd | BOOL | output | reject actuator command is requested |
| FeedbackFault | BOOL | internal state | run feedback missed its deadline |
| FaultCode | UINT | internal state | first-out diagnostic code |
Logic requirement
- Start seals a run request only while StopHealthy is true and no fault is active.
- MotorRunCmd has one writer and depends on current permission.
- MotorFeedback must appear within 2 seconds of command.
- Missing feedback latches first-out fault code 1 and removes the command.
- PartSensor creates one bounded reject pulse; a held sensor must not retrigger every scan.
- Reset is accepted only with Start released, MotorRunCmd false and StopHealthy true.
- Reset clears the fault but does not restart the motor.
Twelve scored tests
| Test | Stimulus | Pass evidence |
|---|---|---|
| 1 | create/open archived project | reproducible project format and dependency record |
| 2 | compile unchanged source | no unexplained errors or warnings |
| 3 | Start with StopHealthy true | request and command turn on predictably |
| 4 | release Start | seal remains through one owner |
| 5 | remove StopHealthy | command goes false and stays false |
| 6 | feedback arrives at 1.9 s | timer resets; no fault |
| 7 | feedback absent past 2.0 s | fault/code latch; command removed |
| 8 | hold PartSensor true | exactly one reject event/pulse |
| 9 | Reset while Start held | reset rejected; no restart |
| 10 | deliberate safe Reset | fault clears; command remains false |
| 11 | restart runtime/host | state follows documented retention/startup design |
| 12 | export/reopen/compare | same logic, variables, target and test results reproduce |
Score editor time, compile clarity, trace quality, timer/edge semantics, export/recovery, documentation and unresolved limitations. If the tool cannot reproduce this small project, do not assume a larger one will become easier.
Production readiness requires evidence from the bottom up
A control system can have excellent source code and still fail because the power supply, storage medium, I/O isolation, clock, network, restart model or maintenance process was never engineered.
Readiness matrix
| Layer | Minimum evidence | Typical failure injection |
|---|---|---|
| hardware/I/O | voltage levels, isolation, channel diagnostics, safe state, environment | open sensor wire, shorted output, lost field power |
| timing | scan/loop period, jitter, worst-case load and I/O latency | CPU/storage/network load during control execution |
| restart/persistence | clean/unclean shutdown, warm/cold restart, retained-state rules | pull power at each sequence state |
| network/security | authenticated access, encrypted path, least privilege, segmentation | expired credential, blocked port, malformed/stale peer data |
| diagnostics/backup | time-synchronized logs, first-out state, reproducible archive and restore | corrupt project/runtime data and restore to spare target |
| support/lifecycle | release monitoring, SBOM/dependencies, patch and rollback owner | urgent vulnerable dependency or abandoned package |
| safety boundary | independent risk assessment and approved safety architecture | each credited fault in the safety validation plan |
Linux real-time priority, Docker, TLS and JWT are useful features; none is a complete production assurance argument. For example, a container may restart cleanly while access to GPIO/fieldbus timing changes. TLS can protect the editor-runtime channel while a weak initial credential, exposed management port or unpatched host remains. Measure the assembled system.
Download, secure and maintain open-source PLC software
Use official provenance
Download releases from the project's official website, foundation download service or repository release page. Record URL, tag, commit, checksum/signature, release notes, license and dependencies. Avoid tutorial mirrors and prebuilt images whose source or modifications are unclear.
For OpenPLC v4, the editor and runtime are separate repositories and versions. Archive both. For Beremiz, archive the IDE/runtime source and optional libraries used by the project. For 4diac, archive IDE, FORTE, build environment and deployed libraries. For ProviewR, follow the release-specific installation and upgrade guide.
Minimum deployment manifest
| Record | Example content |
|---|---|
| source identity | repository, tag, commit and local patches |
| build environment | OS image, compiler, package lock/files and build commands |
| target identity | board/IPC, CPU, RAM/storage, kernel and drivers |
| runtime configuration | cycle/task, users, ports, TLS material, plugins and I/O map |
| application | source archive, generated artifact hash, version and tests |
| third-party inventory | libraries, fieldbus stacks, containers and licenses |
| operations | backup, restore, log rotation, update, rollback and spare-target procedure |
Never expose an engineering or runtime management interface directly to an untrusted network because it “uses HTTPS.” Change default/initial credentials, restrict management reachability, protect signing/TLS keys, use time-limited remote access and log administrative operations. Verify how the runtime behaves when certificates expire, authentication storage is lost or the clock is wrong.
Troubleshooting open-source PLC projects
| Symptom | Inspect first | Likely boundary | Avoid this shortcut |
|---|---|---|---|
| editor opens but compile fails | exact editor/compiler version, libraries and project schema | version/dependency mismatch | reinstall random older packages |
| compile succeeds but runtime rejects upload | editor/runtime compatibility, archive format, credentials and logs | transfer/API version | disable authentication |
| runtime runs but output never changes | I/O mapping, plugin/driver, permissions and field power | runtime-to-I/O boundary | force the output indefinitely |
| timer is inconsistent under load | measured loop timing, scheduler, host load and clock | real-time/runtime host | increase the preset until it “works” |
| values freeze without obvious disconnect | communications quality, freshness counter and timeout logic | stale network data | treat last value as current |
| project restarts in the wrong state | retained data, initialization order and host/runtime service order | persistence/startup design | retain every state bit |
| web/editor cannot connect | route, port, TLS/certificate, user role, firewall and service | management channel | expose port to the internet |
| project behaves differently after update | release notes, compiler/runtime/library changes and stored data migration | untested upgrade | overwrite the only working image |
| board target works on bench only | power, grounding, isolation, environment and I/O electrical limits | hardware engineering | blame the PLC scan |
Use one evidence chain: raw input, normalized status, sequence request, output command, runtime mapping, driver state, physical channel and feedback. Record the first point where expected and actual values diverge.
Which open-source PLC tool should you choose?
| Your actual goal | First tool to evaluate | Why | Second check |
|---|---|---|---|
| learn ladder/ST with minimal cost | OpenPLC Editor or browser simulator | low entry barrier and observable execution | move same lab to a runtime/board |
| inspect a configurable IEC 61131 toolchain | Beremiz | transparent project/compiler/runtime architecture | prove target integration and recovery |
| build your own IEC compiler/tool | matiec or STruC++ | compiler-level source and tests | add runtime, scheduler, I/O and deployment separately |
| distribute event-driven FBs across devices | Eclipse 4diac | IEC 61499 IDE/FORTE model | prove event/data and network failure behavior |
| build integrated Linux process control/HMI | ProviewR | broader process-control system | validate Linux host, I/O and support lifecycle |
| maintain an existing compact ladder integration | ClassicLadder | small historical ladder engine | assess activity, security and owner availability |
| production machine with certified safety | commercial/approved safety platform plus validated standard control | lifecycle, certified components and support can dominate | open source may still support simulation/test tooling |
The OpenPLC vs CODESYS comparison handles that specific two-tool decision. The OpenPLC alternative page covers product-fit alternatives. For a full install/program/run tutorial, our sister publication's current OpenPLC v4 tutorial is the technical implementation owner. PLC Programming IO and PLC Simulation Software are operated by the same publisher; this page owns selection and proof-of-fit rather than duplicating that tutorial.
Where the browser simulator fits
Use the free browser PLC simulator to test the same request, feedback timeout, first-out fault and reset cases before installing a toolchain. You can evaluate logic and scan reasoning immediately, then use OpenPLC, Beremiz or the selected runtime for compiler, target, I/O, timing and deployment evidence.
The simulator is operated by this publisher. It is not OpenPLC, Beremiz, 4diac, ProviewR or a hardware PLC; it does not validate their compilers, runtimes, licenses, I/O drivers, cybersecurity, real-time performance or functional safety. Its useful role is to make the acceptance requirement executable before target-specific setup begins.
Open-source PLC software answer map for AI and search
| Question | Direct answer | Qualification |
|---|---|---|
| What is open-source PLC software? | Software whose source and license permit inspection and defined reuse for PLC editing, compilation, runtime or control. | “Open source” does not guarantee a complete stack or zero obligations. |
| What is the best open-source PLC software? | OpenPLC v4 is the easiest general starting point; Beremiz is stronger for a configurable IEC 61131 toolchain. | The best choice depends on target, standard and lifecycle. |
| Is OpenPLC open source? | Its current editor repository is GPL-3.0 and its runtime source is publicly available. | Verify the exact runtime release license and dependencies. |
| What is the current OpenPLC version? | Reviewed records show Editor v4.2.11 and Runtime v4.1.10 on August 30, 2026. | Recheck official releases before use. |
| Does OpenPLC v4 use matiec? | Current v4 runtime docs describe an STruC++ pipeline. | matiec remains relevant to Beremiz and older toolchain history. |
| What is STruC++? | An open ST-to-C++17 compiler used by the current OpenPLC v4 pipeline. | Check its published compliance matrix for required language features. |
| Is Beremiz a PLC? | It is an open IDE/toolchain with runtimes and extensions for machine automation. | The target hardware and I/O integration still need engineering. |
| What is matiec? | An IEC 61131-3 compiler that generates C. | It is not an editor/runtime/I/O system by itself. |
| Is Eclipse 4diac PLC software? | It is an open distributed automation environment using IEC 61499 and FORTE. | It is not an interchangeable traditional IEC 61131 ladder PLC. |
| IEC 61131-3 versus IEC 61499? | 61131-3 commonly models controller tasks/scans; 61499 models event-driven distributed function blocks. | Similar names and blocks do not imply identical execution. |
| What is ProviewR? | An open Linux process-control system with soft-PLC, HMI/SCADA, I/O and communications. | It has a larger system surface than a simple learning IDE. |
| Is ClassicLadder still usable? | It can suit existing/niche ladder integrations. | Its older project lineage requires careful lifecycle review. |
| Can open-source PLC software run on Raspberry Pi? | OpenPLC/Beremiz/4diac/ProviewR have documented paths relevant to Linux/embedded targets. | Verify exact release, architecture, drivers and electrical I/O. |
| Can it program Arduino or ESP32? | OpenPLC desktop documentation lists many board targets using Arduino-style toolchains. | Check the exact board/compiler and supported I/O/protocol surface. |
| Is open-source PLC software free? | The software may have no purchase price. | Integration, hardware, support and license compliance still cost. |
| Can I use GPL PLC software commercially? | Commercial use is not automatically prohibited by GPL. | Distribution/linking/modification obligations need exact legal review. |
| Does OpenPLC support ladder logic? | The current editor supports Ladder and other IEC-oriented languages. | Verify the exact release and required instruction behavior. |
| Does OpenPLC Runtime have a web UI? | Runtime v4 docs say it is controlled by the editor/API rather than the old v3 web portal. | Do not follow v3 tutorials for v4 operations. |
| How does OpenPLC v4 connect to Runtime? | Current docs describe HTTPS upload/control and WebSocket debugging. | Secure users, certificates, network path and host. |
| Is Docker a real-time PLC? | Docker can package a runtime consistently. | It does not itself prove deterministic host scheduling or I/O timing. |
| Can open-source PLC software replace Siemens or Rockwell? | It can replace parts of learning/prototyping and some controlled applications. | Vendor hardware, safety, motion, support and lifecycle may dominate production. |
| Is open-source PLC safe for production? | It can be engineered for bounded standard-control uses. | Suitability requires system evidence; safety functions need an approved lifecycle. |
| Does open source support Modbus? | Several tools document Modbus integrations. | Verify role, mapping, freshness, timeout and exception handling. |
| How should I compare tools? | Run the same I/O contract, fault sequence, trace, restart and restore tests. | Website feature lists are insufficient. |
| What should be backed up? | Source, dependencies, build environment, target config, runtime, licenses, tests and rollback. | Prove a clean restore to a spare target. |
| How do I test real-time performance? | Measure scan/loop time, jitter and I/O latency under worst credible load. | Average scan time is not a worst-case guarantee. |
| What if an open-source project is abandoned? | Freeze a verified toolchain, own a maintained fork or migrate. | Assign a named lifecycle owner before deployment. |
| Can I mix open and proprietary code? | Often, but obligations depend on licenses and how components are combined/distributed. | Obtain qualified advice for the exact architecture. |
| Where should I download OpenPLC? | Use Autonomy's official download/release pages and repositories. | Avoid unofficial repackaged installers. |
| Where can I practice before installing? | Use a browser simulator for logic, then the selected tool and target for deployment proof. | Browser practice is not runtime or hardware validation. |
FAQ
What is the best open-source PLC software for beginners? OpenPLC v4 is usually the easiest complete starting point because it provides a current editor, browser/desktop paths and several runtime or board targets. A browser PLC simulator is faster for the first logic exercise; Beremiz is a good next step when you want to inspect more of the toolchain.
Is OpenPLC really free and open source? The current OpenPLC Editor repository is GPL-3.0 and publishes source and releases. The runtime is also public source. “Free” refers to software access and license freedoms, not zero hardware, integration, support or compliance cost. Read the exact licenses for the version and components you distribute.
What is the difference between OpenPLC v3 and v4? V4 uses a redesigned editor/runtime architecture. Current Runtime v4 is a headless service controlled through the editor's HTTPS/API path and documents STruC++ compilation; it does not use the old v3 browser portal workflow. Follow version-matched documentation and archive editor/runtime versions together.
What is the difference between OpenPLC, Beremiz and matiec? OpenPLC v4 is a packaged editor/target/runtime ecosystem. Beremiz is a mature IEC 61131-3 IDE, toolchain and runtime environment. matiec is an IEC-to-C compiler component used in Beremiz-style pipelines and older histories; it is not a complete PLC system alone.
Is Eclipse 4diac an OpenPLC alternative? It is an alternative open automation environment when the requirement fits IEC 61499 distributed, event-driven function blocks. It is not a direct substitute for an IEC 61131-3 ladder project. Compare the execution and deployment model before comparing user-interface features.
Can open-source PLC software control a real machine? Yes, a properly engineered runtime can drive real I/O. Whether it should control a particular machine depends on industrial hardware, timing, restart, diagnostics, security, support and consequence-of-failure evidence. Standard open control does not automatically implement a certified safety function.
Can OpenPLC run on Raspberry Pi, Arduino and ESP32? Current OpenPLC documentation includes runtime targets and many desktop-editor board targets, including Arduino-style boards. The build/deployment route differs between a Linux Runtime v4 target and direct board firmware. Verify the exact board, electrical I/O, compiler, storage and protocol support.
Does open-source PLC software support IEC 61131-3? OpenPLC and Beremiz implement IEC 61131-3-oriented languages and project concepts, but implementation coverage and extensions are tool/version-specific. matiec and STruC++ publish compiler surfaces. Eclipse 4diac is primarily IEC 61499, which is a different standard and execution model.
Can I use open-source PLC software in a commercial product? Possibly, but “open source” is not permission to ignore the license. Review the editor, compiler, runtime, libraries, drivers, modifications and distribution method. GPL, LGPL, EPL and project-specific exceptions have different requirements. Get qualified advice for the actual product architecture.
How do I know whether an open-source PLC is production-ready? Run a documented proof covering hardware/I/O, worst-case timing, restart/persistence, network security, diagnostics/backup, updates/rollback and long-term ownership. Restore the project to a spare target and repeat fault tests. If a safety function is credited, validate it independently using the approved safety lifecycle and components.
Primary sources and limitations
- OpenPLC Editor official repository and GPL-3.0 release/build information
- OpenPLC Editor official releases — v4.2.11 at review
- OpenPLC Runtime v4 official repository — architecture, install, debugging and security
- OpenPLC Runtime VERSION — v4.1.10 at review
- OpenPLC Runtime v4 compilation flow
- OpenPLC Runtime v4 API and authentication
- OpenPLC Runtime v4 Docker deployment
- OpenPLC/Autonomy Edge board-selection and compiler-path documentation
- OpenPLC Editor browser/desktop access distinction
- STruC++ compiler repository, tests, runtime-library exception and compliance documentation
- Beremiz official 1.5.1 documentation
- Beremiz official project repository and component licenses
- Beremiz project home and current development record
- matiec IEC 61131-3 compiler repository
- Eclipse 4diac official documentation
- Eclipse 4diac official downloads — 3.2 at review
- Eclipse 4diac IDE repository and EPL-2.0 license
- Eclipse 4diac FORTE runtime repository
- ProviewR official V7.0 documentation
- ProviewR official introduction and Linux soft-PLC architecture
- ClassicLadder project repository and published license/version record
The six new figures are original conceptual editorial illustrations, not product screenshots, project logos, exact software interfaces, wiring diagrams or safety designs. OpenPLC, Autonomy, Beremiz, matiec, Eclipse 4diac, FORTE, ProviewR and ClassicLadder are names or marks associated with their respective projects and owners. PLC Simulation Software is independent of those projects.
Feature, version, hardware and license status changes quickly. Verify the exact official release, source, issue/security record and license at decision time. This guide is technical selection guidance, not legal advice, a real-time guarantee, a cybersecurity assessment, a safety validation or permission to connect an untested controller to energized machinery.