Freeciv is a free turn-based multiplayer strategy game, in which each player becomes the leader of a civilization, fighting to obtain the ultimate goal: To become the greatest civilization.
Gameplay features and specifics:
Actually runs pretty well, while also looking nice. However, if you want to play freeciv online I recommend just playing one of the mirrors of freeciv-web. Other than that it's Civ 2 but you can play as the Hacker nation led by Richard Stallman so 10/10 right there.