The gamemode "Aftermath" is developed by Silverlan, he is the only one who owns and works on this gamemode. This gamemode is based on the game "Fallout3", but using different ideas from The Hl2 Renaissance pack (Created by the same author) and Hl2 and others games. "Aftermath" is a Rpg-like gamemode in which you (will be able to) interact with other players, kill creatures to gain experience, skills, and complete quests. This Gamemode is currently in beta, and is open to the public for now.
This video shows how the companion liberty prime works so far.(It may be in the new renaissance pack wich you can download {when it come out, AND it may not be in the gamemode, I got to find out.} but the one that is released can be download which contains some of the monsters and weapons that this gamemode(Afterlife) will contain.)