FreeCiv is one of my favorite open-source projects out there. Civilization is one of my favorite games, and FreeCiv is an open-source version that you can download and play for free. The latest update of the game has added an HTML 5 version, which means that you can now load up and play FreeCiv right in any compatible browser. And that includes mobile Safari, which means you can now navigate to play.freeciv.org on one of your iOS devices, and play the game at will.
Pretty excellent. There is no version of FreeCiv in the App Store, unfortunately, though there has been a port to Android just recently. And Civilization Revolution has been available on both iPad and iPhone for a while now -- it's a simpler, more accessible version of the 4X strategy game. Firaxis has just recently stepped up its efforts on iOS, so it's possible that we will see a more full, official version of Civ arrive on the iPhone before too much longer. Or wait -- what if they ported Alpha Centauri? Drool.
But until then, FreeCiv will have to do. If you have never had a chance to play, the game manual should help you out.