CoWasm supports WASI right now via this library https://www.npmjs.com/package/wasi-js, which I actually develop as part of CoWasm . One unusually thing I did, which goes beyond what emscripten does, is I implemented a quite a bit of posix functionality, often by writing extension code to nodejs and calling it from Javascript, because there's a lot of POSIX that Node.js doesn't expose. This only works on Mac and Linux and is also available standalone in this library https://www.npmjs.com/package/posix-node, which is implemented in Zig. You can get a sense of the scope of POSIX functionality that goes beyond what WASI defines here: https://github.com/sagemathinc/cowasm/tree/main/packages/ker...

One motivation for doing this is to try to get the full Python test suite to pass, including all the functionality that involves subprocesses, posix calls, etc. I've only got to about 85% at this point. It can be a ton of tedious work, but at least Zig helps impose some discipline (e.g, it doesn't let you ignore handling errors until later), and makes it easy to test compilation for all supported targets on every change (due to excellent cross compilation support).