From their Github
The Battle for Wesnoth is an Open Source, turn-based tactical strategy game with a high fantasy theme, featuring both singleplayer and online/hotseat multiplayer combat. Fight a desperate battle to reclaim the throne of Wesnoth, search for the key to immortality, or take part in any number of other adventures.
Takes a while to install first time due to a ton of extra packages packages and the source code being installed/downloaded.