GPLed Code Libraries
HLib is a general-purpose C++ library developed by me since 1999. It includes a nice poll(2) model for simultanious (non-polling) access to any number of file descriptors, command line args handling and more.
Probably of no use to you if you're not using some Unix (preferrably Linux) or not familiar with the system calls like read(2) and open(2).
QTXlib is a small library for primitive graphic output directly using Xlib from inside Qt-based applications. This allows performance gain of factor 2 and more in special situations such as mass drawings of filled rectangles for cellular simulations and the like.