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.
World Foundry is a 3D level game engine and asset production pathway with over 170,000 lines of code. It was originaly created as a commercial product, but is now being released under the GPL. The engine was designed from the beginning to be cross platform, and ran on Windows (DirectX, GL), and the Sony Playstation. The production pathway ran on Windows, and extended 3DStudio Max to be our level editor. The engine is currently being ported to Linux (it runs, but needs work), with plans to port the production pathway as well. Developers are wanted to help with this effort.
XPilot is a graphical multi-player maneuvering game with less-exciting graphics, but more speed, tactics, and insults. Some people also use it for UDP network analysis. Over the past eight years of playing and development, tons of features have been added to the game, from basic weapons like shotguns and missiles to more recent ones like phasing devices, invisibility, or hyperjump.
Teddy is an OpenGL-based 3D graphics library written in C++. Its main features are simple scene graph and windowing system-enabling multiple cameras, camera windows, and scenes. It focuses on easy and flexible manipulation of models and model materials in the scene graph. It contains a number of primitive objects like sphere, box, and cone, and it can load LightWave object and scene files.
QGolf was developed for radio amateurs to clarify the behaviour of a signal on an antenna. It demonstrates the forces that act on a rope if you move one end of it: you can see how waves are reflected, how resonance occurs, and how multiple pulses coexist on the same rope. Various parameters can be updated during the simulation.
Planets is a fun, interactive program for many-body gravity simulations. The emphasis is on play: it's easy to add in planets, zoom in and out, change the physical constants, save and load configurations, etc. It's designed to be easy enough for a kid to enjoy, but that hardly precludes adults.