I had a hacky script setup that did the appropriate assigns needed to point to different system installations on a single partition. This worked fine most of the time. I could boot between OS4 on my A1200 or OS3.9. It was easily configurable to work with all the kickstarts but anything less than 3.1 needed to be kicked into RAM.
The primary startup script would check a directory and based on which files were present, it'd setup the appropriate system directories and then relaunch S:Startup-Sequence after S: had been reassigned to the new Sys:S directory.
I knew how to use it but it wasn't really in a redistributable form. I thought about writing a small tool to make it better. There are also some files on aminet that will detect if a mouse button is down (left or right) during startup and execute some command if it is. Some folks use this as their trigger to load another OS.
