KeeperRL

KeeperRL is a dungeon building strategy game with roguelike elements. There is a commercial version with non-free assets, and a gratis version, which is functionally the same, but with only ASCII-style graphics (which is under a free license). Only the ASCII version is a completely libre game.

Similarly to e.g. OpenDungeons the player takes a role of an evil wizard building a dungeon with traps and creatures. It is possible to take control of the creatures, which makes the game play like a classic roguelike game (e.g. NetHack). Players can also play as adventurers exploring dungeons made by other players.