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this post was submitted on 13 Jun 2026<br>3 points (100% upvoted)<br>shortlink:

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Apple Lisa Emulator in Rust and WebAssembly - The Machine That Thought It Was 1983 AgainShowcase (i.redd.it)

submitted 31 minutes ago by Adam_Jesion<br>comment<br>share<br>save<br>hide<br>report

I built a browser-based Apple Lisa emulator in Rust, with a lot of help from autonomous Codex/Claude loops. It works beautifully.

That is the part I still find hard to believe. The Apple Lisa emulator I have been experimenting with is now running LisaOS in the browser. Not as a mockup, not as a video, not as a skin over somebody else’s local emulator, but as a hardware-level emulator written in Rust, compiled to WebAssembly, and launched directly from a regular web browser.

As far as I can tell, this is the first Apple Lisa OS emulator of this kind: Rust, WebAssembly, browser-based, and usable without setting up a local build environment. You open a page, give it a moment, and you are suddenly sitting in front of one of the most important computers of the early 1980s.

What makes this project especially interesting to me is not only the emulator itself, but the way it was built. A large part of the work was done through autonomous Codex loops. I defined the goal, collected every technical document I could find about the Lisa hardware, ROM behavior, memory map, disk protocol, MMU, and boot process, then let the agent work toward a very concrete objective: get a visible LisaOS desktop in the framebuffer with working input.

Piece by piece, it decoded the machine.

It was not magic in the cinematic sense. It was much stranger and, honestly, much more impressive. The agent read documentation, wrote debugging tools, inspected logs, made hypotheses, patched the emulator, ran it again, failed, found the next broken assumption, and kept going. The process looked a lot like a human engineer doing reverse engineering work, except that much of it happened autonomously, in long loops, while I was doing other things. I guided it a few times, mostly when it got stuck conceptually, but the core of the experiment was to see how far a well-scoped autonomous coding loop could push a genuinely difficult systems project. The answer, at least in this case, is: surprisingly far.

The emulator now runs with the original ROM, but it also has a ROMless architecture, which I call HSL emulation. That matters because the Apple Lisa ROM still does not have an open license. I did not want this to be a project that depends on casually passing around someone else’s ROM binary and pretending the legal issue does not exist. The ROMless layer lets the emulator boot without requiring the user to copy the original ROM.

The disk side...