The Mac client just launched in beta form and is available as a download both for current players and as a trial for new players. It's expected to be out of beta this fall, when players using the Mac client will receive a couple of custom titles ("I'M AN ORDER" and "I'M A DESTRUCTION") and an in-game trophy called the iPomme.
Also, you should probably know that this client is only good for the game's North American players. A client for European players is said to be available "soon."
For more details on hardware specs and to download this thing, check out Mythic's download page for the client.