In my previous post I discussed the relationship (or lack of it) of video games and the Free Software ideology. While the majority of games must exist in a commercial environment for meaningful development to be possible, there are of course many community based projects as well. Here's just a couple interesting ones I've run into. I'm only covering games that are entirely Free Software here, which don't rely on any proprietary content
id Software released the Doom engine source code, which has led to countless ports and improved versions for many different systems. The content of the original game, however, is not free. Freedoom provides a free replacement for the data. In combination with a Doom engine port it is, essentially, a whole new game with new graphics, monsters, maps and everything. What's more, it allows you to play many of the countless Doom maps and mods available on the net.
Another interesting entry on the FPS front is OpenArena, which basically does to Quake 3: Arena what Freedoom does to Doom. Fast paced deathmatch against bots or online, just the thing to kill half an hour on a boring day.
While the previous are basically free content for engines of originally commercial games, there are of course entirely original projects as well. One interesting example is The Battle for Wesnoth, a traditional turn-based fantasy strategy game. The overall quality is at least on par with classic 90's representatives of the genre and there are many campaigns to play, in addition to downloadable user-created content.