CrossOver lets Windows apps run on OS X, sans Windows CodeWeavers plans to release a Mac OS X Version of its WINE-based CrossOver application this summer.  CrossOver doesn't require a full version of Windows running in emulation... rather, it uses the open-source WINE project to run individual Windows applications just like any other app on your Mac.  Word is, the apps run about the same as they would on a Windows computer.  Theoretically, PC games would run fine, too, but it's not certain this will be the case in reality.  If CrossOver works as advertised, it would be even a step above Parallels Desktop in making it simple to run Windows apps on the Mac.  Besides convenience, CrossOver would be less susceptible to Windows viruses since there's no actual Windows OS running.