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.
Zombie Master is one of my old favorites. The notion that one player truly can screw over and control the experience for a team of humans as they complete dynamic objectives is just as fun as it sounds. Sadly, the community has all but died at the point of this review, but a remake/sequel is in the works by a separate modder.
ZM in its hay day was some of the most genuine fun you could grab out of a mod.