Survivor 3D is a retro-style FPS game created in CopperCube 6, inspired by Half-Life and Quake. The game is very buggy (intentionally). It contains 12 chapters, that will take you about an hour to finish.

Backstory:

There is an ongoing fight between two militias: The Security Phasing Combat Militia (SPCM) and The Ammo Trait Combat Militia (ATCM). You're Ken Newman, part of the SPCM.

The conflict is over the owner of the Bachs Underground Establishment (BUE), a gigantic complex of tunnels, bunkers, offices, etc. It is wanted because it contains such powerful generators, so many advanced devices, but the most important thing: a dimensional portal. 

You're one of SPCM's best soldiers, but you were sent to fight as the last soldier of theirs (and you were also shot in your hand a few months ago, so you still struggle to pull the trigger). You are a miracle to this fight, as you kill every ATCM enemy on your way. Your objective at the start is to destroy the portal the ATCM came for, and then leave. 

You quickly find out how big the BUE actually is. The ATCM is powerful, and they have a lot of soldiers to fill the BUE with, in order to stop only YOU.