Mac OS XMacOS X, the next version of Apple's highly proprietary OS, was not based on the Copland development project, but on a cross with NeXTStep called Rhapsody (which up to Dev release 2 was available for PCs), and is designed to have the friendly MacOS graphical layer over 4.4BSD on top of Mach. It features a way of running current MacOS software through the "carbon" API and the "classic" boxed environment.
Here is a good page about finding real OS software for Apple's machines.
Conversely, ARDI is selling a MacOS emulator for PCs (more or less System 6/7 compatible): Executor. You can also find a good, free one for BeOS and Linux (LinuxPPC) called SheepShaver. Mac-on-Linux also works.