Battle for Wesnoth is a turn-based fantasy strategy game. Various races - humans, elves, dwarfs, drakes and undead - and various factions battle for the control of the land of Wesnoth in various eras.
The strategic gameplay is similar to games such as Master of Monsters and Warsong. The players, represented in game as high-level commander units, recruit new units, who then fight, advance in experience and eventually turn to another units.
There's both a multiplayer mode, which typically involves wiping out the enemy (or at least their commander). For single player games, there are several campaigns as well as ability to play multiplayer mode against the computer. Also included is a map editor and a scripting language to construct new campaigns.