WASI Libc is a libc for WebAssembly programs built on top of WASI
system calls. It provides a wide array of POSIX-compatible C APIs,
including support for standard I/O, file I/O, filesystem manipulation,
memory management, time, string, environment variables, program
startup, and many other APIs.

WASI Libc is sufficiently stable and usable for many purposes, as
most of the POSIX-compatible APIs are stable, though it is continuing
to evolve to better align with wasm and WASI.