Other interesting bits for the Mac to maybe recover would be Mach Ten,
which ran Mach on top of regular MacOS. (Talk about inverted pyramids...)
Interesting (not sure I would say 'cool'). I saw running it once next to NeXT Cube when I was visiting some friends in the Mach group at CMU at some point. I had always been under the impression it just used MacOS 7 to load it and then took over the system. But I never ran 'under it' as it were.
There was also a Mach/Linux that I think ran on the Mac at some point.
I think I remember seeing that announced.