I believe it's just a patch. Buy the Classic version and then download and install the patch. Then have fun playing in OS X. Make sure you have a supported video card like a Radeon or GeForce2/3, or you will not be able to run the game under X. I believe the demo is Os X compatable already, so you can download and test to make sure your system is up to spec. You can get the demo from Apple's Os X download section of their web site. Look under games, or just do a search for Oni once your in the download section of their site.