This seems appropriate for an off-topic thread. Let's have ourselves a list of other freeware (open or closed) game projects out there. I'll post the ones I feel are worth mentioning here.
The Battle for Wesnoth is one of the better known ones out there. Many people love it, but I didn't enjoy it much. If I want a strategy RPG, I'll take Langrisser or Fire Emblem. Oh well.
Cube is a freeware FPS. It's a lot like Quake 1, except the engine is totally different. For instance, you make maps in-game. You can even make maps in multiplayer, which you have to admit is cool. Though Cube isn't being developed anymore, its spiritual successor Sauerbraten is.
FreeOrion is an open-source clone of Master of Orion 2. Development is slow, but it looks promising.
Iter Vehemens ad Necem is a roguelike RPG. It looks slightly better than ordinary roguelikes.
King's Quest IX is a fan-made sequel in the world famous King's Quest series. They were shut down by Vivendi, who owns the KQ copyrights, but then they were granted a licence to continue.
DOOM Legacy is the best freeware port of DOOM out there. Ideal for people like me who dislike modern FPS games, and prefer the old stuff in a new environment.
Mind Arms, a Japanese fighting game. Well, it's not that good. But it's free.
Scorched Earth 3D. What it says. Scorched Earth, except in 3D. If you don't know what Scorched Earth is, you're square (and if you REALLY don't know, it's the game Worms was based on).
Space Quest 7 is like KQIX, except with Roger Wilco. Development is progressing steadily, and at this rate it might be done somewhere in the twenty-fifth century.
Transcendence is a rather crappy game similar to Escape Velocity. On the upside, unlike Escape Velocity, it's freeware. Unlike Escape Velocity, it's not written for the Mac.
Ultimate Stunts is a remake of the classic game Stunts. It doesn't work very well, though. The (commercial) Trackmania is a lot better if you want a stunts-like game.
Vega Strike is a space simulator like Privateer and X/X2/X3. Some day, it might be really good, but I kind of doubt it.
There are also any number of freeware point-and-click adventure games available on
http://www.bigbluecup.com/Furthermore, there are many roguelikes and some MMORPGs that are freeware, but as I'm not interested in games like that I'll leave it to other people to link to them.