When Apple Built a Mac OS Running on Top of Solaris and HP-UX
The 1990s had a lot of weird stuff like this - platforms, operating systems and software were exploding, and nobody really knew what the end result would be so they focused on ensuring they had a hand in everything.Running Mac OS and Mac OS apps using MAE on Unix workstations was one example.
But there were others too - some I remember are NeXT on Solaris with OpenStep, Mac LC systems that had a DOS compatibility card (486 CPU) to run DOS/Windows apps, and Unix SysV running in Mac OS using A/UX.