One of the images showed Half-Life character Gordon Freeman wearing iMac colors and a partially obscured Apple logo on his chest, while another starred Alyx Vance from Half-Life 2 reenacting Apple's iconic 1984 super bowl commercial by throwing a crowbar at a screen portraying the series' villain Dr. Breen. There's also Francis from Left 4 Dead talking about "hating" different, Heavy from Team Fortress 2 appearing in the classic iPod ad silhouette, and a Portal sentry next to a TF2 turret parodying the "I'm a Mac... and I'm a PC" adverts.
It seems likely that all of these titles will make their way to Mac systems along with the Steam client. What's more, this might be an indication that Valve has ported their Source game engine over to OS X, which would allow any future games based on this engine to be easily launched for the Mac. A formal announcement is expected during the 2010 Game Developers Conference, scheduled for next week, from March 9th to the 13th.