The initial announcement of Steam for Mac conspicuously omitted the inclusion of the first Left 4 Dead game. The Left 4 Dead blog, however, confirms that the original game will migrate to Mac along with the rest of the announced Valve games in "late Spring." The post makes it sound as if both games will be added at the same time, but that remains unconfirmed. Because of Valve's Steam Play technology, you'll be able to play either game on either Mac or PC, with the ability to share your progress between the two platforms.

Even better, you'll be able to play with other people across platforms! "Mac and Windows players can go head-to-head," Valve notes in the announcement, "since both Left 4 Deads are cross-platform compatible. Mac owners can even host their own servers and create their own maps, just like Windows users." Cross-platform play means that all of these new-to-you Valve games are going to come with massive built-in communities.Left 4 Dead 1 & 2 to feature cross-platform play between Mac & PC