Today, not only Valve released "The Sacrifice" expansion pack for Left 4 Dead 1 and 2, but Left 4 Dead 2 is now available for Mac owners.

Left 4 Dead 2 is the sequel to Valve's 2008 award-winning, co-op game. Set in a zombie apocalypse, you play as 4 new survivors and go through cities, swamps, and cemeteries of the Deep South shooting or hitting zombies to the "uncommon" infected such as the Mudman.

Right now, it is 50% off of both the original and its sequel ($6.79). The Left 4 Dead 1 + 2 Bundle is $10.19 with the 50% discount.