Wesnoth

[battlestar]

The Battle for Wesnoth is a turn-based tactical strategy game with a high fantasy theme.
Battle for Wesnoth

Build up a great army, gradually turning raw recruits into hardened veterans. In later games, recall your toughest warriors and form a deadly host whom none can stand against! 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.






Further information: Description - Wesnoth

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Disclaimer: I am not part of the game development team, though I do user-made work using the game.

 

[Telcontar]

I've played it. Even contributed a few bugfixes a couple years back, but never got more actively involved in the development. It's a great freebie for turn-based strategy fans.