Open games are pickup games where you can meet new people, and do not need a group to play.
Zombie Missions are occasionally hosted that follow one of two different gameplay styles
Option 1. "Haunted"
Zombies are defended against by survivors, with fixed HP
Great for zombie shoot house's or L4D type games
Option 2. "Apocalypse"
Missions are setup where the players have to accomplish the mission while being attacked by hoards of zombies! Don't let them get to close though, getting hit by a zombie will get you infected, and possibly turn you into a zombie on the spot, forcing you to switch teams, and attack your friends!
Games are First come First Serve.