Mac OS X PowerPC emulation is spotty at best.
Mac On Linux?
Runs the PowerPC Mac OS X on PowerPC Linux systems.
Most that I know of aren't emulators but virtual machines for the PowerMac/CHRP platform that happen to run the PowerPC Mac OS X on them.
There would be more I am sure, and for Intel Macs, but Apple can just threaten lawsuits to discourage more of it. If the ability to run Mac OS X apps on other platforms exists, Apple stands to lose a lot of money on hardware sales. The Hackintosh market, for example uses cheap PC hardware to run Mac OS X on a non-Apple branded computer.
I did install OSX 10.2 Jaguar a couple of weeks ago on PearPC because my son is obsessed with the different releases that came out before he was born. I wanted to show him all that pin-stripey goodness.
They of course would have to buy a chip maker that can make 64 bit ARM CPUs with at least quad core to save on costs. I think Apple wants to get rid of buying chips from Samsung because of the iOS vs. Android lawsuits.
All assuming, of course, that Apple is interested in such a purchase.