Aftermath is a hl2 mod which involves the player killing waves of the undead with your friends or alone using weapons, your knife or even blow them up with grenades and set them alight with Molotov's.
this is a tutorial that will help you setup hammer for zombie survival, there may still be some entity that shouldnt be there but they will be gone in...
this tutorial will allow you to install the prefabs to hammer, they may not be great and if use chack the outputs of the trigger as it uses a client command...
this tutorial will show you how to create zombie spawns for zombie survival.
This tutorial will help you create buyable weapons for zombie survival.
This tutorial will help you setup a server for ZS:multiplayer when it is released