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.
Well it has been a while, but here is a big update that you will like. As you already have guessed Silverlan has created another type of gamemode that has to do with your survival. This new gamemode that was created will make players have to work together so they may live the incoming waves of onslaught.
In this gamemode there are specific types of characters each having their own unique weapons and skills that help and contribute to the team. Each class has their own Perk, Specialty, Weapons(sorry about the repeat here), Speed, Health, and each having their own set of Skill Points that each class may or may not have.
and last but note least, Sharpshooter.
Additional information is given when selecting the characters with in the gamemode (which I have not played so I have little info on this, I am sorry about this lack of information for each character.)
FYI: There is also a slow-mo system implanted in-game already that occurs when someone gets a good shot it on an enemy, so be advised to enjoy the good shoot out when it happens.
(I do not know if it is like so but) There is also the patience of having to wait for your team to win or lose because once you die, you must wait till the wave is over so that you may return to the living to fight of the next wave or start over. With the addition of a store system, so when the wave is complete you may go and purchase goods like stempacks, and ammunition that is needed to be ready to survive the next wave.
In the beginning of it all, it is pretty much very easy but with each wave there is an increase in enemy count and their durability. So if you think that one shot kill on that ghoul would be all you have to do, then you got something coming to you then.
There are two gameplay videos that you may want to check out when I upload them to get plenty of info, if you have any questions then don't be afraid to pm me so that I can clear things out. Thank you for your time and I hope this will get things flowing again for a bit.