Team Fortress 2 Mann vs. Machine Co-op Mode Launched

You must stop a lethal horde of robots from deploying a bomb in one of Mann Co.'s many strongholds
Valve has announced that Mann vs. Machine (MvM), a new co-operative game for its free-to-play online action title Team Fortress 2 (TF2), is now available to download for free via Steam on PC and Mac.
MvM lets you and five friends fight a lethal horde of robots on all-new maps, with the opportunity to upgrade abilities and weapons along the way. You will band together to survive all of the robot waves in a variety of missions to earn incredible loot and unlock new achievements.