It’s probably worth mentioning that you can also use QEMU, which is a bit more involved but can use a bigger disk and also run OS X, and Mac OS 9.2.2 (as it supports an MMU, SheepShaver doesn’t)
Is QEMU the best option to run older OS X (in particular Snow Leopard, and yes, a legal retail purchased physical copy) on a modern machine? I currently keep a rather bulky cheese grater to run a few programs from time to time.
That's the option with the least headache. I believe there are other simulators too but they are much more specialized.
With some hacking you can run all MacOS/MacOS X versions on x86, x64 and PPC from 8.6 to 13 if you have a x64 machine. If you have an Apple Silicon one it gets too slow to simulate around 10.10 (on x64 you can use hvf virtualization). It might be a bit less nice than tailored emulators like SheepShaver but having the same UI for all these OSes (plus other OSes) beats everything in my opinion.
Unfortunately Apple Silicon machines cannot be simulated without some hidden knowledge only some secretive companies have. Hopefully the knowledge will become public some years from now.
My memory is that it only had to be run on Apple hardware, but perhaps I should go back and check. Or just not tell anybody, and hope the Apple Police don't get me — it's not like I'm letting something that old out to play on the internet (though I do sometimes miss iCab).
Unfortunately qemu isn't as 'integrated' as Sheepshaver -- theres the mouse grab problem, also no disk sharing with the host (the read[/write] fat32 disk don't seem to work, at least under 9.2.2)
I had a a project for #marchintosh of making myself a nice powerPC emulation stack to recompile and open source quite a few free/shareware I did back then, but I more or less gave up as I couldn't find something 'comfortable' to work in. I guess I'll have to find, dust up and try to hook that old G4 Mac Mini that I'm sure is in a drawer, somewhere :-)
You can, but not under BeOS. Under BeOS Mac OS is run almost like Classic was on MacOS X. The OS is more or less virtualised as a user space app, and the CPU is not emulated in any way. That’s the main reason that BeOS only supports PowerPC. Indeed, if you run it on a Mac under BeOS it doesn’t even need a toolbox ROM