Übergame is a free open source, realism like, multi-purpose, multiplayer, casual, first-person-shooter game.
Standalone direct download: https://www.uebergame.com
Or get it on Steam: https://store.steampowered.com/app/391780/Uebergame/
Manual (also available ingame): https://duion.com/games/uebergame/manual/main
Source code available at: https://github.com/Duion/Uebergame
And source code for the Uebergame engine: https://github.com/Duion/Torque3D
Instructions how to compile the game or playtest development builds: https://duion.com/games/uebergame/playtesting