I created (and play), a browser game called Crimelife. Its a fast-paced mobster game. And in the spirit of free games, there are no paid items or plans. Everyone has the same free account. I have tried creating open source games in the past, but Crimelife is my only "real" success. My friends love it.

Feel free to play, and look for me in the game. My username is "Godfather". ;)

What's your favorite linux game?

For me, it's a tie between Tremulous and Nethack. B)