If you’re looking for a high quality, open source, turn based strategy game, look no further than Wesnoth.
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.
Fight to regain the throne of Wesnoth, of which you are the legitimate heir, or use your dread power over the Undead to dominate the land of mortals, or lead your glorious Orcish tribe to victory against the humans who dared despoil your lands â€¦ Wesnoth has many different sagas waiting to be played out. You can create your own custom units, and write your own scenarios â€“ or even full-blown campaigns. You can also challenge your friends â€“ or strangers â€“ and fight multi-player epic fantasy battles.