Today Valve software is bringing Steam game distribution platforms to Mac OS, which is going to change gaming on Macs.  The library of games that Valve software includes are “Left 4 Dead 2, Team Fortress 2, Counter-Strike, Portal, and the Half-Life series” and supposedly Portal 2 will be released simultaneously for the Mac and for Windows.  According to Valve, “Portal 2 will be Valve’s first simultaneous release for Mac and Windows. ‘Checking in code produces a PC build and Mac build at the same time, automatically, so the two platforms are perfectly in lock-step,’ said Josh Weier, Portal 2 Project Lead. ‘We’re always playing a native version on the Mac right alongside the PC. This makes it very easy for us and for anyone using Source to do game development for the Mac’ ” [via MacRumors].

So while you are getting ready for Steam on your Mac OS, here is a Left 4 Dead 2 trailer: