If you want to try out the Oberon language, there are several Oberon implementations for different platforms, including embedded systems, native windows executables, and the Java virtual machine: http://oberon07.com/compilers.xhtml
I feel not having anything on a runnable state from System 3 or AOS doesn't do proper justice to Oberon.
Those versions were already quite close to something like NeXT, but with Oberon variants.
Nowadays what is left are random ISOs that don't always boot properly on VMs and it isn't easy to compile the those OSes, even with some source still floating around on Github.
