Nexuiz is a free open-source first person shooter that runs on Windows, Linux and OSX. It's a 3d deathmatch game that has been in development since the summer of 2002.
For a lot of programmers, writing an application is fun, but writing its manual is not. Adding new features, refining the product, and responding to users' input are all more rewarding than writing instructions on how to use the software. However, good documentation is necessary to have happy, informed users who can contribute meaningfully to future development. A few months ago, Gilbert Ashley, the author of src2pkg (Slackware's "magic package maker") invited me and two other people to help him manage the user documentation for his program. The process we used to create the src2pkg wiki may be a useful example for other free and open source software (FOSS) application developers.