The Battle for Wesnoth

The Battle for Wesnoth is free and open-source turn-based tactical strategy game with a fantasy theme. More than 200 unit types, 6 major factions,16 nations, and hundreds of years of history. 54 different languages are supported, including Bulgarian ;)

You can play in single player or in multi-player (up to 8 players are supported, different channels supported, including Internet)
There is a map editor. You can also create new units, campaigns and scenarios.