I haven't played Warsow in years, so I don't know what state the game or community is in. It's a fast paced FPS multiplayer that turned the old bunnyhopping exploit into a central feature iirc.
Frets on Fire! It was the cool open-source equivalent to Guitar Hero. And you know what - it was pretty hecka cool to wield your keyboard like a guitar.
My favorite: cataclysm dda, flare rpg, oolite.
Space Station 13 is great
Which of these are available on Android?
I have F-droid, and Ive installed Mindustry and Open Transport Tycoon Deluxe.
Mindustry is great for wasting time.
Battle For Wesnoth is on android, the controls are kinda wonky but it's not bad.
Unciv is pretty cool and portable.
Sauerbraten
OpenRCT (not totally free but a damn impressive project nonetheless)
OpenRCT is free iirc! You can just get the RCT2 demo for the assets OpenRCT needs
KeeperRL is a lighter Dwarf-Fortress like game where you play as a Monster making a Dungeon.
Barotrauma is source available (no commercial, public use, restricted for game modding and contributions) Librerama is dumbways to die style minigames
xevil
ClassicUO is a nice open source client for Ultima Online. Need to have the game assets.
Fragsurf
Taisei Project for Touhou and other 2D bullet-hell shooter fans (I recommend installing it instead of playing online).
zero-k is really good rts. Its similiar to supreme commander
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