I think Apple licensed MacOS to run on Mac clones (the open 'Common Hardware Reference Platform') for a short time, but then freaked out because they weren't making as much money that way, and stopped licensing for the CHRP boards. Motorolla and Power Computing (maybe some others?) made Mac clones for a short time.
At the time Apple killed CHRP off, there was a version of Windows NT in development for it, which was cancelled.
