The Battle for Wesnoth is a Free, turn-based tactical strategy game with a high fantasy theme, featuring both single-player, and online/hotseat multiplayer combat. Fight a desperate battle to reclaim the throne of Wesnoth, or take hand in any number of other adventures. Easily modifiable. You can even download other users' add-ons from the main menu.
It's one of my all-time favorites due to his easy to learn controls and the nice upgrading of your units.I was profoundly happy to find it on Desura cause that means I don't have to manualy update any longer :-D