Musl

musl is a C standard library intended for operating systems based on the Linux kernel, released under the MIT License. It was developed by Rich Felker to write a clean, efficient, and standards-conformant libc implementation.

Overview
musl was designed from scratch to allow efficient static linking and to have realtime-quality robustness by avoiding race conditions, internal failures on resource exhaustion, and various other bad worst-case behaviors present in existing implementations. The dynamic runtime is a single file with stable ABI allowing race-free updates and the static linking support allows an application to be deployed as a single portable binary without significant size overhead.

It claims compatibility with the POSIX 2008 specification and the C11 standard. It also implements most of the widely used non-standard Linux, BSD, and glibc functions. There is partial ABI compatibility with the part of glibc required by Linux Standard Base.

Version 1.2.0 has support for (no longer current) Unicode 12.1.0 (while still having full UTF-8 support, more conformant/strict than glibc), and version 1.2.1 "features the new 'mallocng' malloc implementation, replacing musl's original dlmalloc-like allocator that suffered from fundamental design problems."

Use
Some Linux distributions that can use or do even use exclusively musl as the standard C library include Alpine Linux, Dragora 3, Gentoo Linux, OpenWrt, Sabotage, Morpheus Linux, Chimera Linux, and Void Linux. The seL4 microkernel ships with musl. For binaries that have been linked against glibc, gcompat, glibmus-hq. can be used to execute them on musl-based distros.