Rocks!

libressl
This was created as a response to crazy levels of pointless complexity (like reimplementing their own malloc system) in the core cryptography library almost all linux and bsd programs use openssl. They cleaned all the code up and untangled it.


 * http://www.libressl.org/

musl libc
This is a complete reimplementation of GNU libc. A few linux distros are using it completely. Having a second alternative implementation of libc helps pull things back to the POSIX specifications.


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

sbase/ubase
This is a complete reimplementation of the GNU coreutils. The source code is shorter and tries to be simpler. They also fix a lot of oddities and bugs in details (like the tr program).


 * http://core.suckless.org/sbase
 * http://core.suckless.org/ubase