Dota 2 has been released for Windows users everywhere. Despite a vague indication of there being a Mac release to happen at some point, no further mention of it UNTIL NOW.
Today, the “test” version of the game became available on the Mac version of Steam, and a post was made on Reddit:
You should be able to go to http://store.steampowered.com/app/570/ and select “GET DOTA”. When you’ve gotten access to Dota, it should show up as “Dota 2 Test” in your Steam games list.
We are currently testing on Dota 2 Test, so the main Dota 2 product does not show Mac or Linux support. Getting access to the main Dota 2 product will also give you access to the Dota 2 Test product.
The game is a sequel to a Warcraft 3 mod that spawned an entire new genre (the most famous of which is probably League of Legends). The game is free to play, but has a monstrous learning curve in spite of the relatively simplistic gameplay. You can provide feedback on the Mac version via the developer forums or at Github.