Today they just announced that Guild Wars 2 has a client for Mac OS X which is available for download right now, though it is in beta.

Today we’re happy to announce another major milestone in the development of Guild Wars 2: going forward, ArenaNet will also be supporting the game on Apple’s Mac OS X. The Mac Beta client is available immediately for all Guild Wars 2 players. It shares the same features and connects to the same live game servers as the PC client. Anyone who purchases Guild Wars 2 can now play it on both PC and Mac.
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The Mac Beta is available to anyone who has purchased or purchases Guild Wars 2. All you need is an active Guild Wars 2 account to download the Mac Beta client. Just log in to account.guildwars2.com and click Download Client to get started. If you have any questions, check out our Mac FAQ.