Wine is an implementation of the Windows API on top of X and Unix. It does not require Microsoft Windows, but can use native Windows DLLs if they are available. It provides both a development toolkit for porting Windows source code to Unix as well as a program loader, allowing many unmodified Windows programs to run on x86-based Unixes.
Doom was the classic 3D shoot'em'up game from id Software. PrBoom is a game engine for playing Doom levels, which runs on both Windows and Linux/Unix systems. It uses the SDL graphics library. PrBoom a very faithful Doom port, with great effort taken to be compatible with as many original Doom levels and demos as possible.
CHEOPS (CHEss OPponent Simulator) is a fully-functional AI chess program capable of human vs. human, human vs. computer, and computer vs. computer play. It uses a 64-square linear array board representation. The game tree search is alpha-beta, and the static evaluation function considers material, mobility, and motif features. CHEOPS comes with extensive documentation on the program internals, aimed at students or programmers wishing to understand or extend the system.
The Castle is a first-person shooter game in a dark fantasy setting. Your main weapon is a sword, so the fight is mostly short-range. Three main levels are included, packed with creatures, items, and sounds. A couple of bonus levels are also available, like the classic DOOM E1M1 level reimplemented in VRML. The game engine is based on VRML, OpenGL, OpenAL, and all shadows are done by the shadow volumes approach.
Xye is a puzzle game in which the objective is to get all the gems in each level. The mission is not as easy as it sounds: there are traps, monsters, and very hard puzzles everywhere. The player can interact with objects in the game in a lot of ways, and some of the objects can also interact with other objects.
ZDoom is an enhanced port of the official DOOM source. It features support for all Hexen editing features (including ACS, hubs, etc.), support for most BOOM editing features, freelook, jumping, and translucency support, a Quake-style console, high screen resolutions, removal of the original DOOM's limits, support for many more music formats (including MOD, IT, XM, S3M, MIDI, MP3, and MUS), better mouse support, UDP networking, and more.
Berusky is a logic game that is based on an ancient puzzle named Sokoban. The old idea of moving boxes in a maze has been expanded with new logic items such as explosives, stones, special gates, and so on. In addition, up to five bugs can cooperate and be controlled by the player.