MachTen runs as a background accessory on MacOS. Apparently it’ll turn on mmu protection if you have one.

But you are still able to run macOS software just fine.

A/UX boots macOS, then loads a loader app that takes over the machine and boots the kernel. The emulator Shoebill “cheats” and reads the kernel from the UFS disk directly and jumps to that.

Previous (the emulator) runs all the versions of nextstep for the 68k machines but also supports the true colour card, along with i860 emulation.

It’s pretty impressive what can be done with processors in the multiple GHz range with megabytes of l2/l3 cache.

From: TUHS <tuhs-bounces@minnie.tuhs.org> on behalf of Clem Cole <clemc@ccc.com>
Sent: Monday, July 20, 2020 10:30 PM
To: Aharon Robbins
Cc: The Eunuchs Hysterical Society
Subject: Re: [TUHS] A/UX [was Linux is on-topic]

On Mon, Jul 20, 2020 at 4:49 AM <arnold@skeeve.com> wrote:

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.