Some language -> WASM -> C -> Cosmopolitan C Compiler -> Actually Portable Executable that runs on just about anything...?
Or better yet Some Language -> MLIR.
But it turns out many languages do have "Some Language -> WASM" now. WebAssembly brings portability to the table.
No, it's not exactly the same amount of portability as some language and its native toolchain. If you give me source code in some language that I can transpile to C or C++, or into WASM (and then into C), then I can give you a single file which can be executed on Linux, BSD, Mac, or Windows.
That's not remotely the same thing as "its native toolchain."
You, a developer or tech savvy person, might not see any difference.
But if I hand a non-tech-savvy person a file and they can just run it, no matter what OS they're using - with no pre-requisites - that's kind of magic.
Using what libraries & syscalls? A portable IR and a portable executable are very different things, yet the WASM crowd loves to conflate them. WASM is only a portable IR, it doesn't get you portable programs at least not if you want your program to do anything beyond a trivial hello world.
And for Cosmopolitan Libc, there's documented Functions:
https://justine.lol/cosmopolitan/functions.html
And if you want to see things beyond a trivial hello world, you can check out some examples:
https://github.com/shmup/awesome-cosmopolitan
https://github.com/burggraf/awesome-cosmo
Or you can see a pretty big list of pre-compiled Actually Portable Executables here: