Valve Corp. has released Left 4 Dead 2, its popular zombie action game, for the Mac. The game is available for download exclusively through Steam, Valve’s popular game download service, and is available at a special price, $6.79, for a limited time.

[ad#Google Adsense 300×250 in story]Left 4 Dead 2 is the sequel to the original Left 4 Dead, a horror first person shooter that puts you squarely in the middle of the zombie apocalypse. You and friends travel through cities, swamps and cemeteries in the deep South across five campaigns as you try to survive.

The original Left 4 Dead is similarly available for $6.79, though it’s not yet available for the Macintosh (it’s widely anticipated to be released before the end of October, however). If you already own Left 4 Dead 2 through Steam for the PC, you can download Left 4 Dead 2 for the Mac for free.

System requirements call for Mac OS X 10.6.4 or later (Snow Leopard Graphics Update required), 2GHz dual core Intel processor, and ATI Radeon 2400 or Nvidia 8600M or better 3D graphics.