The Battle for Wesnoth is a turn-based strategy game with a fantasy theme. Build up a great army, gradually turning raw recruits into hardened veterans. In later games, recall your toughest warriors and form a deadly host against whom none can stand! Choose units from a large pool of specialists, and hand-pick a force with the right strengths to fight well on different terrains against all manner of opposition.
Official Site: http://www.wesnoth.org