0 A.D. (pronounced "zero ey-dee") is a cross-platform real-time strategy (RTS) game of ancient warfare. It's a historically-based war/economy game that allows players to relive or rewrite the history of ancient civilizations, each depicted at their peak of economic growth and military prowess.
Armadillo adventure is an adventure game set within a world. It is a codebase, a toolkit for making your own adventures such as King's Quest. The toolkit has an example adventure program that can be easily changed and enlarged by derivation. If you are more interested in dungeoneering games, take a look at the <a href="http://freshmeat.net/projects/tanirs-quest/">Tanir's Quest</a> project.
C-Dogs SDL is a port of the old DOS arcade game C-Dogs to modern operating systems. C-Dogs is an arcade shoot-em-up which lets players work alone or co-operativly during missions, and against each other in the "dogfight" deathmatch mode. The original DOS version of C-Dogs came with several built in missions and dogfight maps, and this version is no exception. The author of the DOS version of C-Dogs is Ronny Wester.
Chocolate Doom is a Doom source port which aims to behave as closely as possible to the original DOS Doom executables ("Vanilla Doom"). It aims to be compatible with DOS Doom demos, configuration files, savegames, and bugs. As far as possible, it provides the same features that are available in the DOS version, along with the same "feel" of the original game.
CorsixTH is a clone of Theme Hospital. As computers evolve, we risk losing some classic games. Bullfrog's Theme Hospital, published in 1997, is a classic simulation game, but getting it to run natively on modern operating systems is getting progressively harder. CorsixTH aims to reimplement the game engine of Theme Hospital, and to be able to load the original game data files. This means that you will need a purchased copy of Theme Hospital, or a copy of the demo, in order to use CorsixTH. After most of the original engine has been reimplemented, the project will serve as a base from which extensions to the original game can be made.
Forge has more than 3,000 cards and allows to you play the trading card game Magic: The Gathering against the computer with rules enforcement. Other formats include drafting, sealed deck, and the "quest mode" where you start with a basic deck and you win more cards. The AI and user interface are basic but usable.
GLoid is a 3D block game inspired by Arkanoid. It was originally written as an SDL and OpenGL exercise, but has developed into a full-featured, highly playable game with refined graphics and sound effects. It runs equally well on Windows, Linux, and Mac OS X, and has minimal hardware requirements.