Based on the EDuke32 game engine, NBlood is a new open source port of the classic FPS Blood. From what Voidpoint (Ion Maiden) said on Twitter, it's using their version of the game engine too.
Showing some good post-release support, Kite Games and Kalypso Media Digital have pushed out a free content update and a new DLC for the strategy game Sudden Strike 4 today.
City Game Studio from Binogure Studio will have you run your own game development company, this one was actually developed on Linux using Godot Engine and other FOSS tools.
While 9 Monkeys of Shaolin did have a pretty big delay, Sobaka Studio have just recently announced a new release date (including Linux support) along with help from Koch Media.