I used to play openarena (Q3a ish) a lot. And we had some group games of freeciv. I never got torcs to work well enough to play. That would have been great and simulation would be the perfect kind of "game" to free / open source. And countless hours of nethack on every platform I had (which was a few). Other roguelikes too. Ones that actually are like rogue, that is. Even rogue.

But all that was a long ago. Should maybe explore more.