Are there any multi-user VR worlds out there that are usable from a Mac? I'm thinking something like ActiveWorlds or There, neither of which are supported for the Mac -- either social or game-based, but no war games or museum-on-a-web-page VRML type things. I used ActiveWorlds several years ago on a roommate's computer, and I'm seriously thinking of getting VirtualPC just for that, but I'm hesitant since that's probably the only thing I'd use it for.