Looks like it's a fork of emscripten augmented to compile a whole OS kernel and userland. Includes raylib for graphics, and Lua bindings to it so I feel at home. Seems easy to build so I'm comfortable depending on the hosted version.
There's an app store anyone can publish apps to. Your changes remain in your browser's local storage until you publish them. All apps in the app store are mounted on the file system under /usr/store so it's easy to look at their source code.
Here's a port of one of my early LÖVE apps, for geometric constructions. It's on the app store so anyone should be able to run it just by clicking on this link.
Disclaimers. It's slow. Still lots of bugs. I had to reboot the VM several times while recording this video. Commands often hang or crash, then completely stop working until I reload. It's never lost my data, though. (Data is stored in local storage.)
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