Barony, a pretty cool looking 3D first-person roguelike has opened up the engine under the GPL license and is now on github.
Note: While the engine is now open source, the assets are not. You still need to own a copy to use the now open source engine.
See the announcement here.
I really do wish more developers did this. It can really help a project, as plenty of people would be willing to help out lots of games get better Linux support for free because they like it.
Find Barony on Steam and the github for it here.
About the game
Barony is a 3D, first-person roguelike with cooperative multiplayer that brings back the cryptic and intricate designs of classic roguelikes such as Nethack and melds them with RPGs like Ultima Underworld, System Shock, and Daggerfall. Challenge is the calling card of this hard-boiled dungeon-crawler.
About the author - Liam Dawe