Valve's Left 4 Dead

The PC zombie shooter, from the creators of Counter-Strike, is a co-operative multiplayer game based on the Source engine and using version 2 of Turtle Rock's artificial intelligence technology.

"By leveraging its industry-leading AI technology and years of Counter-Strike development experience, Turtle Rock is building upon the elements that make Counter-Strike successful and applying them to Left 4 Dead," said Gabe Newell, co-founder and president of Valve. "What Counter-Strike did for multiplayer action games, Left 4 Dead will do for co-op games."

Left 4 Dead is expected to be released in 2007.