BZFlag is a 3D, multiplayer, tank battle zone, capture the flag game that pits players against each other in a networked environment. It runs on Windows 95/98/NT/2000, Linux, MacOS 10.x, Irix, Solaris, and others. An OpenGL accelerator is highly recommended, but it is playable with 3D in software.
Dreams Eternal is an FPS game that focuses on a strong story line and puzzle solving. It is set in the dream world. The very short summary of the story is that a scientific experiment went wrong and everybody is stuck in the dream world. You have to end this experiment by hopping from dream to dream. In every dream you have to find clues to try to find out how the experiment can be aborted.
Glt is a library of C++ classes and routines for programming interactive 3D graphics with OpenGL. The aim of Glt is to augment the OpenGL API with convenient mechanisms for manipulating the OpenGL state machine. Glt is a work in progress, and by no means covers the entire OpenGL specification. However, it already includes several useful classes and is designed so that additional classes can be added easily. In addition to Glt, the GlutMaster classes provide C++ wrappers for the GLUT API.
libGLOOP (GLOOP is Liquid Object Oriented Particles) is Brian Sharp's implicit surface rendering demo boiled down into a reusable library. libGLOOP uses OpenGL to render implicit surfaces defined by "meta-particles", and is useful for modelling liquids, volumetric rendering, and other related fields.
libksd is a cross-platform (C++) game framework which is built on top of SDL and also uses libSigC++ for its signal system. It provides drawing functions, a simple widget set, multi-threading, plug-ins, collision detection, joysticks, image loading/saving, simple audio playing/loading/saving, true-type fonts, and some other stuff too.