[hoosierham]

I fear systems so dependent on computers that nothing can be done;in my view there should alwys be a way for actual human control.Nor is this total interconnection a good thing.People don't realize just how vulnerable we are to some evil computer terrorist.

For your most obscure 4th OS,you might try Amiga OS !

[Still Thinking]

I actually ran into a large industrial router not too long ago running on OS/2! The manufacturer wanted some ungodly amount for a Windows version of their operating software, so we had to deal with it as is.