This is a gamemode called Underdone 13.
It was an RPG originally created by the Shell Shocked Gaming and Tower Yard Entertainment Team for Garry's Mod 12.
It has now been remade and fixed to work on Garry's Mod 13 by The Commander.
The popular gamemode UnderDone from Garry's Mod 12 is now available on Garry's Mod 13 for public beta testing. Ironically called Underdone 13 You can...