Pirate101 is adapting the game to a native Mac client, with the test realm version of the client available now. Players will be able to download and install the game at their leisure, although the new client is not currently hooked up to the live servers.
There's no need to sign up for the testing, but not everyone is eligible. Active members and players who have made at least $6 worth of purchases in the last 30 days may download and try the new client; free-to-play players may not. Still, it's easy to become eligible if you really want to jump into some Mac-based piracy, so you can free your computer from having to run at least one game via Boot Camp.