Freeciv, a famous Civilization clone, got an official update to v2.1.4. It's a free, turn-based multiplayer, meaning you play a move and wait for the opponent to play his. You'll be leading your civilization all the way from the Stone Age and up to modern times and space travel. This new Freeciv version contains numerous fixes, especially for stability issues.
You can play Freeciv on LAN, as well as the Internet. The game contains pre-made maps and scenarios, whereas the game contains over 50 units and 100 nations you can choose to lead. The game also features 29 languages as well as many other options.
You can download it here.