Ask HN: Most useful C libraries?

[gaalze]

What are useful/less known C libraries you want to share?

A very useful list (for me) is: http://wiki.musl-libc.org/wiki/Alternative_libraries

throwaway2001 is the one I'll use to introduce a few

[throwaway2001]

http://www.musl-libc.org/

[throwaway2001]

http://rr-project.org/

[throwaway2001]

http://valgrind.org/

[throwaway2001]

https://lttng.org/