GreenteaOS – brand new operating system reaches alpha Windows .exe support

Greentea OS is an alpha-stage, GPL3 desktop OS from scratch that boots from zero to Solitaire**.exe** in 2s+ on an average laptop.

Hey there, fellow programmer! I'm PeyTy, the guy who kicked off Greentea OS back in 2016. It started as a vision: what if we built an open source OS that runs .exe files like Windows, but feels like sipping a warm cup of green tea?

Or maybe like something that has a decent, fully GPU-accelerated compositor at 240 fps GUI, yet offers infinite backwards compatibility and speaks of software preservation without blinking?

Fast forward to July 2025, and we're in alpha — running apps like Solitaire, Minesweeper (including the very original XP version!) and a Calculator with a slick, as cozy as you want GUI. Now, we need you to help us brew something truly epic.

Greentea OS is our love letter to desktop computing. It's a 64-bit OS for x86 (and in the future ARM64 and RISC-V), designed to run everyone's favorite Windows .exe files natively — no emulation, no overhead. Our Tofita engine (built from scratch, not NT or UNIX) powers a lightweight, user-friendly experience. Think of it as open-source Windows cousin, with a GUI that feels like home and performance that pops for gaming or productivity.

And the secret sauce? It's all written in Hexa, our custom programming language that's as easy to pick up as a pencil.

Tofita Engine

"Monolithic" game-engine-like preemptive kernel written in Hexa, 2 GB RAM floor, boots via UEFI on a real HW, with a lightweight sandboxing

Caramel

Native .exe compatibility layer, Tofita-only, basically a bag of .dll files, while Tofita offers PE32+ loader and NT-like syscalls (but we do not strictly follow NT design), bonus point: NT drivers support is a must (of course) and is in the prototyping stage

After years of prototypes we reached GUI apps compatibility in July 2025; basic GUI-less apps were supported for a longer time.

The development process was intentionally quiet until things cross the proof-of-concept stage. Now everyone can see that creation of a new OS from scratch is within reach of the humanity. Yes, people like you and me can create an operating system. No magic, no unicorns, only code and compiler. Just the collaborative power of individuals building something groundbreaking.

I was skeptical until I saw Solitaire for the first time working on the Greentea OS. That hit me especially hard, as I was implementing GDI function by function and it suddenly worked. We've been always told that OS dev is so hard that only aliens (or corporations) would make one... This is now debunked.

Project was aiming at two specific issues up to this moment: see if its possible and then make it possible to survive to the completion.

The strongest challenge was gaining knowledge. Well, long story short, with emergence of AI and tools like Ghidra it's not an issue anymore. Modern hardware is also well standardized and predictable.

Another one was... patience and determination. This one is solved by sacrificing me, PeyTy, to do the most boring "make something that works and THAN we will start talking" part. You're welcome.

Everything else? Mostly typing the letters in the computer and reading a book or two.

If you're not familiar with the term below, Vertical Slice refers to creating a fully functional, representative portion of a project that demonstrates all layers of the project's functionality (from acquiring framebuffer from the UEFI, slicing it with the DWM, down to the GDI function drawing on it)

This issue was tackled with a Vertical Slice approach. Through-and-through. Like, seriously. Even the most terrible code was part of the simulacrum. Most generative SOTA AI models were also evaluated for their supposedly destructive nature (i.e. simulation of a scenario where most people on the project are vibe coders). Multiple programming paradigms, languages and patters were tried.

The research report will be shared later, for now you may observe the seemingly chaotic nature of the codebase up to this point.

Here, at Greentea OS, we feared stalling like other OS projects. The fundamental proactive assumption that such project is doomed to fail caused us to carefully evaluate all the pit falls, known history (even the most obscure projects - you cannot imagine how many people tried to create a Win-like OS before and still try), old and modern programming approaches. Lot's of the research were incorporated into the Hexa design (and more to come), while most of it is yet to be systemized and applied.

The chaotic codebase will be cleaned up soon (like that 7000-line extras.hexa), but I wanted everyone to see it for historical purposes

Hexa is designed to make coding Greentea OS fun and approachable, not a headache like C++ can sometimes be. Here's a peek at what you could easily read and write:

This could be a button in our GUI — simple, right? Hexa powers everything from Tofita's low-latency process management to our cozy buttons, and embraces safety by design — even when you do not focus on it explicitly.

Made with balanced human-oriented design, minimizing cognitive strain, yet safe, as fast as C++ and quick to compile. We currently transpile into C and C++ due to lack of time dedicated to the project, expect at least an LLVM target too

With Hexa, you'll write clean, expressive code to shape an OS that millions could use.

Hexa wasn't created specifically for a Greentea OS, its was designed for making game engines, which - surprisingly - have lots in common with the osdev. So here we are, using Hexa for purely technical reasons. Hexa also crosses PoC right now, docs will be updated on-demand.

• Make a Mark: Fix a TODO comment, tweak a button's look, correct a typo, or boost .exe compatibility — every contribution brings Greentea OS closer to being the open source Windows alternative.
• Join a Warm Community: We're not about gatekeeping or drama. Whether you're passionate about kernel development, GUI design, or .exe compatibility, join our crew.
• Be Part of a Larger Picture: We just got Solitaire running in July 2025. Next? Maybe your code runs Notepad++ or a game. Imagine a happy user, maybe even your loved ones, using them.
• Grow Your Skills: Learn Hexa, dive into the Caramel compatibility layer, or experiment with our Tofita engine. It's a playground for coders with a fearless innovation: we welcome multiple implementations to see what's work better.

Greentea OS isn't just code — it's a community, a vision, a vibe, an art in a software form, depending on what you want and how you see it. We do not enforce any agenda on you and we follow the collaborative GPL license to keep things open and fair, as we're all about collaboration, not competition (shoutout to our friends at ReactOS!). Whether you're fixing a bug, designing a window, or dreaming up a new feature, your work will shape an OS that feels like home.

So, grab a virtual cup of tea, fire up Hexa, and let's build the future together. Ready to make Greentea OS the coziest, most powerful OS out there? Let's do this, one commit at a time!