skalibs is a package centralizing the public-domain C development files I use for building other software: it contains essentially general-purpose libraries. You will need to install skalibs if you plan to build skarnet.org software. The point is that you won't have to download and compile big libraries everytime you need to build a package: do it only once.
skalibs can also be used as a sound basic start for C development. There are a lot of general-purpose libraries out there; but if your main goal is to produce small and secure C code, you will like skalibs.
skalibs contains exclusively public-domain code. So you can redistribute it as you want, and it does not prevent you from distributing any of your executables.