GLGraphics is a library for the Processing programminglanguage that offers a number of classes to simplify the handling of OpenGL textures, GLSL shaders and off-screen rendering inside Processing.
XreaL is a heavily improved Quake 3 Arena engine. It's bundled with new tools and a demo game that was never finished. ET:XreaL is a subproject bringing all XreaL enhancements to Return to Castle Wolfenstein: Enemy Territory.
Slut is a programming framework for generative, synthetic, interactive, network-enabled graphics. THIS IS AN OLD PROJECT. But since you are interested in it you should check out the SceneExpression project: http://labs.nortd.com/sx/
Simple Ray Tracer is a platform independepent 3D rendering engine using a technique known as Ray Tracing. The programminglanguage is c++ and the code is object oriented, very simple, and intuitive. It provides a great foundation to learn ray tracing.