Can one even dual-boot different MacOS versions?
How many methods would you life ?
Firstly, as long as your hardware supports the OS versions you want, you can install different systems in different disk partitions (and/or on different disks) and dynamically select which one to boot from. That's "built in" and needs nothing extra.
Or, you can use VirtualBox, Parallels, (some others I can't recall), and run one OS as a guest in the other. I have quite a few Parallels VMs for different tasks - even one running DOS, though I forget what I needed that for now.
Biting the hand that feeds IT
