Other Open Source Games

What are your favourite open source game ever you played beside Thrive? Write your favourite open source game here.
As example: I like playing Naev, Endless Sky (not now again), FreeOrion, Vega Strike, and Pioneer Space Sim.


I too have played Naev and Endless Sky (my computer can’t run it without lag anymore, though). I got bored of them after a while. I really enjoyed certain musics tracks in Naev (there was one that sometimes played while fighting and it was one of my favourites).
I’ve also played Minetest, but after a few minutes of playing it alone, I normally get some existential thoughts. “What should I do with my in-game life? I could build a house… or dig for a bunch of minerals… Does any of that have any meaning? What has intrinsic value? If such a thing were not to exist, why should I continue playing this game? What keeps me from ending my in-game life?”. I normally quit once I get that far.
I also play Mindustry. I avoid public servers due to the frequent (or very harmful) griefing and due the fact that my latency varies between 600 and 1100 ms. I also don’t play on private servers that much, since I don’t really have many humans to play with. Singleplayer gets a bit boring after some time.
I also enjoy playing Cataclysm: Dark Days Ahead. I like the how detailed it is and how free one is. I would find it cool if there was a game with the same theme, content and ideas with multiplayer support. The way it’s currently written makes that impossible (to have multiplayer).