Proplib
This is a C library for the Parallax Propeller. There is not very much documentation for it yet, but what there is is in the doc/ subdirectory. It aims to be (mostly) C99 compliant.
The license is in LIB_LICENSE.txt. Most of the code is under an MIT style license and copyrighted by Parallax and/or Total Spectrum Software. Some is public domain, some is BSD, and the C++ code and libgcc are GPL with a special exception. (libgcc and libstdc++ are not actually included here, look for the Propeller gcc distribution for those).