Left 4 Dead 2 has been available on the Mac since the launch of "The Sacrifice" DLC. All Left 4 Dead and Left 4 Dead 2 DLC is included for free on the PC because Valve is like that.
Left 4 Dead Released for Mac, On Sale Again
Author: Brian Leahy,
published 14 years ago,
The Mac version of Left 4 Dead is now available, fulfilling Valve's promise to launch the Mac version before Halloween. It supports Steam Play, which means that owners of the PC version will snag a shiny Mac copy if they are equipped with an Apple machine.It also means that Mac players will be able to play on the same servers as the PC players. To celebrate the launch, gamers can pick-up Left 4 Dead for $9.99 (50% off) or bundled with Left 4 Dead 2 for the low, low price of $14.99--though not as low as the previous sale.