I was very impressed with Rise of Industry last time I took a look at this strategic tycoon game from Dapper Penguin Studios. They have another big update out along with an announcement about leaving Early Access.
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.
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.