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.
One of the best Free and Open Source turn-based strategy games around - Hell, it bests commercial offerings at every turn, unless you're looking for the latest 3D graphics. A long development history plus a comprehensive toolkit means that there are tons of campaigns for you to play, all for free! Download to your heart's content new campaigns that contain new artwork (much of it anime-style), units and more. Up for a multiplayer session? Play online in multiple configurations; lots of races and classes from which to choose! Easy to learn, difficult to master! If you enjoyed Fire Emblem or Shining Force titles, Battle for Wesnoth will bring back many fond memories.