Following the official launch for Windows earlier this month, Valve's, er, Dota clone Dota 2 is now available for Mac and Linux. This sentence is a hilarious joke about how Linux users are already well-prepared for complex systems with unfriendly communities, but Mac users are in for a hell of a ride. Laughs.
Having done away with invites, Dota 2 is simply up for download on Steam.
If this is your first foray into Dote 'em ups, the guide Welcome to Dota, You Suck is a fair introduction, and that title is a fair hint of what to expect: you will suck. Valve recently added in-game tutorials to ease players in, which I highly recommend you play. But it's fine, you'll learn, and Dota 2 is so amazing I'll be furious when it inevitably isn't crowned Shacknews Game of the Year.
Valve's big annual tournament The International 3 is coming up, running August 7-11 with the finest Dota 2 teams in the world. Anyone with Dota 2 will be able to watch it for free in-game through the awfully impressive spectator system, which offers commentary and statistics and all that jazz.