In case you missed it last night, Valve has turned its excellent team-based shooter Team Fortress 2 into an entirely free-to-play experience, so even if you haven't picked up the game yet, you can head over to Steam right now and download and play it completely free, forever. The game was one of the biggest titles Valve brought over when Steam was made compatible with the Mac, so it's 100% OS X seaworthy -- just install Steam and you're good to get the game.
Valve says it will be monetizing the title through the purchase of in-game items, but they're all cosmetic or conveniences at this point, so you only need to pay if you want to wear a fancy hat or don't want to wait to build up an item. In short, Team Fortress 2
