August 17, 1977
Scattered groups of zombies infiltrate remote Midwestern towns. Incapable of using tools or weapons, the invaders are resisted until they retreat back into the desert. Special elimination posses are set up to hunt down any of the surviving undead. Six weeks after the squads started their search-and-destroy mission, the last known zombie was shot and killed.
Present-day
Over thirty years had passed when a truck driver traveling down a desolate Arizona road plows into a wall of undead. Before the driver's phone signal went dead, he reported some were carrying guns... They're back and now they are hunting us.
Steam Exclusive Features:

Local and On-line Coop — Take on the horde and earn perks together
Barricade Mode — Defend your base against zombie attack
Over 100 Steam Achievements and a dozen Leaderboards
30 Additional Steam User-designed Perks
Xbox 360 Controller support for single or multiplayer
Steam Hammer — Rips the skin off your opponent (nice)
New Steam User designed weapons — Minigun, AA-12, MP5, Beretta 93R, Super Shorty and more
New Levels and New Enemies — Zombie patients and caretakers in a desert asylum, Brawler boss zombies, Suicide bomber zombies..
Pneumatic Destroyer — Detonates the Rammer they are surrounded by zombies

Key Features:

Ultra Fast Action — Fight armies of hundreds of zombies and their bosses in an exceptional close-quarter battlefield experience
Deadly Weapons — Use machetes, axes, jack hammers, dual Uzis, flame throwers, grenades, poison and a dozen more including a Steam Hammer, exclusive to Steam purchasers
Customize Yourself — 100 player modifiers combine with two dozen power-ups for limitless gameplay
Four Game Modes — Free Play, Survival, Barricade and 18 increasingly brutal missions await
Zombies with Guns — They wield axes, cut-off saws, AK-47s and more

Nation Red achievements