Mac OS X

Based on a BSD Unix kernel, with Apple's Aqua user interface, this is one of the best computer operating systems available, providing stability and security while remaining easy to use. The only major drawback is that it is designed to run only on the severely limited selection Apple hardware which is very underpowered and overpriced compared with the competition.

Mac OS X (Apple)

Hackintosh.com For installing OS X on non-Apple hardware.