Before Left 4 Dead had come out, the GameCamp kids and I spent months playing Zombie Master, a great little Half Life 2 mod that combines the point of view of an FPS survival with a simplified RTS Zombie Master. I wanted to create an amusement park level. These were two of the concepts I'd done for a "Frontierland" area. They were going to be simple old world store fronts. Then....L4D2 came around and Dark Carnival made the whole thing a little moot.