Zombie Master is a multiplayer Source modification, centred around a zombie-apocalypse, which throws all but one player in the shoes of human survivors. Pitched against a relentless tide of rotting flesh, they must scavenge for weaponry and equipment just to stay alive. But that one player, chosen randomly at the beginning of the round, is not bound by mortal restraints. To speak his name is to invite the wrath of hell - but most call him the 'Zombie Master'. He is nigh omnipotent. His invisible hand controls the legions of undead like puppets on strings; slowly closing the net on the humans while they run to and fro like rats in a maze.
An entirely original mod that seperates the two sides: the Survivors and the Zombie Master, who can control the zombies as they spawn and use traps (depending on the map) on other players. It was a blast to play with friends, as long as the servers were up. Right now it can still be just as fun, but only as long as there are others to play it with. I suggest you grab some friends, start a server and play several rounds.
All in all, Zombie Master has always been and always will be a personal favorite. It's the game you remember, but it's the times that have changed.