I mention this because I got a hit for it in my referrer list (along with Googles for "Petula Clark Connery Arse" and "Best Looking Scrotum") and that lead me to a page on Wikipedia with a list of open source games:
Open source games are computer games assembled out of, and are themselves, open-source software and open content. For freely available games without or with a partial public license.
Essentially, then the are free. There's versions of Civilization, SimCity and Chess. And an update of Master of Orion that looks better than the offically released MoO III.
Also linked on that page is another page offering a list of commercial games released as freeware. So, more free games that you once had to pay for. It's all, as they used to say, good.