Battle For Wesnoth

David White who started Wesnoth back in 2003, had a vision of a free open source strategy game that had very simple rules, uses a strong artificial intelligence, challenging and fun. Wesnoth has already passed the 1 million mark for downloads. As of March 2007, the game is available in 35 different languages.

A normal Wesnoth player has

200+ unit types
16 different races
6 major factions
to choose from. Actually, you can even make your own custom units, design your own map, scenarios or even campaigns. It’s all up to your creativity. The most interesting part of any game is the ability to multiplay. You can challenge up to a total of 8 friends in multiplayer fantasy battles.