Steam for Mac is officially available, along with a sizeable trove of games - including Portal, which is now free for everybody.
Valve's plan is to release a new set of games for Mac every Wednesday for the next few weeks. This week, notably, every game has SteamPlay, which means you buy it once, and it'll run on all Steam-supported platforms (which implies that not every Steam game available on Mac and PC will necessarily be SteamPlay style). I know, games have existed on the Mac for a long time. But the promise of true multiplatform computer gaming on the largest scale in a long time is pretty thrilling. (As someone who does most of their FPSing on a desktop PC and owns a Mac laptop.)
I honestly can't tell you how hard it is not to pee my pants right now (and I just went to the bathroom).
Right now, there 63 games/gamepacks listed as being available for Mac - Torchlight, Civilization, the LucasArts action pack, among others - though no TF2 in sight, for now. (Though I'm still chaffing that it shoves your game files inside of the Documents folder.) As noted, Portal's only free until May 24, so get in there. Here's the full list on Steam's site:
TriJinx: A Kristine Kross Mystery World of Goo Zuma Deluxe Sid Meier's Civilization IV And Yet It Moves Braid Escape Rosecliff Island Civilization IV: Warlords Civilization IV: Beyond the Sword Sid Meier's Civilization: Colonization Sid Meier's Civilization: The Complete Edition BRAINPIPE: A Plunge to Unhumanity Diaper Dash® Machinarium Football Manager 2010 Bob Came in Pieces KrissX Sam & Max: The Devil's Playhouse Galcon Fusion Quantz Torchlight Toki Tori Valerie Porter and the Scarlet Scandal Parking Dash The Nightshift Code Nightshift Legacy: The Jaguar's Eye Mahjong Roadshow Hotel Dash Suite Success DinerTown Detective Agency Fitness Dash Gemini Lost Atlantis Sky Patrol Fairway Solitaire Professor Fizzwizzle and the Molten Mystery Unwell Mel My Tribe Tales of Monkey Island Complete Pack Osmos Wandering Willows Wedding Dash 2: Rings Around the World Zenerchi Dream Chronicles: The Chosen Child Diner Dash: Hometown Hero Cooking Dash Chocolatier: Decadence by Design LUXOR: Mah Jong The Dig LOOM Indiana Jones and the Last Crusade Indiana Jones and the Fate of Atlantis City of Heroes: Architect Edition Peggle Nights Luxor Luxor 3 Portal Peggle Deluxe Bejeweled 2 Deluxe Bookworm Deluxe Chuzzle Deluxe