ioquake3 (or ioq3 for short) builds upon id Software's Quake 3 source code release. It cleans it up, fixes bugs, and adds features. Its goal is to be the Quake 3 distribution upon which people base their games and projects. Its design goals include optimizing the engine for playing Quake 3: Arena, Team Arena, and all popular mods. This distribution of the engine has been ported to many new platforms. While it doesn't have PunkBuster (and never will), it does provide more security for servers and clients by way of various bugfixes which aren't in id's client.
swampex (or Swamp Explorer) is a cross-platform library designed to work with raster maps in Ozi Explorer format. Using this library, you'll be able to collect maps in the file system, get information about map calibration, find maps by latitude/longitude, render maps in SDL surfaces, and more.
The Brick Engine is a fast and simple lo-fi gaming engine. The engine provides a comprehensive API, including dazzling visual features, song playback, and collision detection: everything you need to make games with quickness and ease. The engine provides a straightforward C API and has language bindings for Tcl and Pascal, with support for more languages on the way.
Blood Makes the Grass Grow Green (BMTG3) is a multi-player, side-scrolling, 1-dimensional strategy game that pits two people against each other in a duel over a stretch of land. Each player is positioned in a bunker at opposite ends of the map and tasked with deploying the right personnel and vehicles to capture FOBs (forward operating bases) and overrun your enemy's bunker. Currently there are 5 different units available. Timing, unit selection, and basic strategy are all necessary for success.
SDLbits is a very lightweight SDL wrapper for Java. This library was designed to be very small and simple. It does not use Swig, but goes directly from "native" Java definitions to the sdlbits C wrapper library to SDL or OpenGL (in C). All symbols are exposed as they would be in C, except the "SDL_" prefix has been removed, since all names are inside the SDL class. The SDL structures from C are translated to very simple Java classes, such as SDL.VideoInfo. Most fields are exposed as read-only "get" methods, but "set" methods for writable members are supported as well. These classes simply interface to the actual C data with a ByteBuffer "pointer".