Open-Source PLC Software: OpenPLC, Beremiz and matiec Explained
Open-Source PLC Software
Open-source PLC software lets you program a real, working PLC in the standard IEC 61131-3 languages without paying for a licence. The hub of the ecosystem is OpenPLC — a free, GPL-licensed editor and runtime that turns a Raspberry Pi, an Arduino, an ESP32 or a plain Linux/Windows PC into a soft PLC. Underneath sit two long-standing projects: Beremiz (the IDE OpenPLC's editor is built on) and matiec (the compiler that turns IEC 61131-3 code into something a machine can run). If you want to learn automation, build a hobby controller, or run a small custom rig without licence keys, open-source PLC programming software gets you there for the price of the hardware.
This guide explains what each tool actually does, how the open-source PLC stack fits together, what languages you can write, and — honestly — where open source fits and where a commercial platform still wins.
What "open-source PLC software" actually means
A PLC program needs three things: a place to write the logic (an editor), something that turns that logic into executable form (a compiler), and something that runs it against real inputs and outputs (a runtime). In the commercial world all three are bundled into one paid suite. In the open-source world they are separate, readable, modifiable projects you can use for free.
- OpenPLC — the most popular open-source PLC. A free, GPL-licensed package with an editor, a cross-platform runtime, and a web-based monitoring interface. It runs on low-cost hardware and talks Modbus.
- Beremiz — a mature open-source IEC 61131-3 IDE. The OpenPLC Editor is built on the Beremiz lineage, which is why the two look and feel related.
- matiec — the open-source IEC 61131-3 compiler. It takes Structured Text and the other standard languages and produces C, which is then built into the runtime. It is the engine quietly doing the translation under both Beremiz and OpenPLC.
The key takeaway: you do not have to assemble these by hand. OpenPLC packages an editor (Beremiz-derived) and a matiec-based toolchain together so you can download one thing and start programming.
How the open-source PLC stack fits together
It helps to see the path your program takes from keyboard to physical output.
- You write logic in the editor (Ladder, Structured Text, etc.).
- The IEC 61131-3 compiler (matiec) translates it to C and builds it.
- The compiled program loads into the soft runtime on your board or PC.
- The runtime drives real hardware — directly on a board's pins, or to remote I/O over Modbus (RTU or TCP).
That last point matters: OpenPLC uses Modbus heavily, both to read and write its own I/O and to act as a master or slave on a wider network. If you understand Modbus, you understand most of how an open-source PLC talks to the world.
What hardware open-source PLC software runs on
OpenPLC's whole appeal is accessible hardware. The runtime is genuinely cross-platform, and the editor runs on Windows, Linux and macOS.
- Raspberry Pi — the classic OpenPLC target; a full soft PLC with real GPIO.
- Arduino (Uno, Mega and similar) — programmed as a remote I/O node.
- ESP32 / ESP8266 — low-cost Wi-Fi-capable boards for small builds.
- Linux or Windows PC — a "soft PLC" with no dedicated hardware at all.
You wire I/O directly to the board, or expand it over Modbus. The total cost of a working controller can be as low as the price of a single-board computer.
IEC 61131-3 language support
Because open-source PLC software is built around the IEC 61131-3 standard, the programming model is the same one you would meet on a commercial PLC. That is what makes it a legitimate way to learn.
OpenPLC and Beremiz cover the standard 61131-3 languages — Ladder Diagram, Function Block Diagram, Structured Text, Sequential Function Chart and Instruction List. Coverage of the fundamentals is solid; what you give up versus a top-tier commercial suite is the depth of advanced libraries (motion, certified safety, large fieldbus stacks) and polished vendor tooling, not the core language model.
Open-source vs commercial: the honest trade-offs
Open source is not "free CODESYS." The two solve different problems, and pretending otherwise leads to bad decisions.
Open source removes the licence barrier and gives you the source code, low-cost hardware and total freedom to modify. Commercial platforms charge for a deep, supported, certifiable ecosystem that is already proven on industrial controllers — vendor support, safety certification, version-locked runtimes and the assurance the same code behaves identically across many brands of hardware. For a classroom or a one-off build, the open-source freedom usually wins. For a production line that must run for a decade with guaranteed support, the commercial ecosystem usually earns its cost.
Is open-source PLC software right for you?
Ask what the project really needs. Learning, prototyping or a low-stakes hobby build? Open source is an excellent, free choice. A regulated machine that needs vendor support, functional-safety certification and long-term spares? A commercial platform is the safer call — and you can still learn the concepts on open-source tooling first.
When open source fits — and when it doesn't
The pattern is consistent: the closer you get to a critical, supported, certifiable industrial deployment, the more the commercial ecosystem earns its licence cost. The further you are toward learning, experimenting and building cheaply, the more open source shines.
Where a browser PLC simulator fits
There is one more piece worth knowing about. Before you install OpenPLC or wire up a Raspberry Pi, the fastest way to actually learn IEC 61131-3 is to write logic and watch it run — no toolchain, no hardware, no setup.
That is exactly what a browser PLC simulator gives you: write ladder logic and Structured Text, run it instantly, and switch dialects to see how the same program looks in IEC, Allen-Bradley and Siemens naming. Because the simulator and OpenPLC both follow IEC 61131-3, the skills carry straight over. Many people use a simulator to learn the language alongside an open-source runtime — practise in the browser, then deploy to real hardware. If you are weighing your options, our OpenPLC alternative page and our OpenPLC vs CODESYS comparison go deeper on where each tool fits.
FAQ
Is OpenPLC really free? Yes. OpenPLC is open-source software released under the GPL. The editor, the runtime and the source code cost nothing to download, use commercially, or modify — your only spend is the hardware you choose to run it on.
What is the difference between OpenPLC, Beremiz and matiec? OpenPLC is the complete package (editor plus runtime plus monitoring). Beremiz is the open-source IEC 61131-3 IDE that OpenPLC's editor is built on. matiec is the open-source compiler that translates IEC 61131-3 code into C so it can be built and run.
What hardware does open-source PLC software run on? OpenPLC runs on a Raspberry Pi, Arduino, ESP32/ESP8266, or as a soft PLC on a plain Linux or Windows PC. I/O is wired to the board directly or expanded over Modbus.
Can I use open-source PLC software in production? You can, and people do for small or non-critical systems. For regulated, safety-critical or vendor-supported industrial machines, a commercial platform is usually the safer choice because of certification, support and proven long-term hardware availability.
What languages can I program in open-source PLC software? The standard IEC 61131-3 languages: Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), Sequential Function Chart (SFC) and Instruction List (IL).