I don't mind sam, but I prefer smit. What we really hated was the benighted C compiler: just ANSI compliant enough to be ANSI compliant, but still require bizarre hacks to compile. Part of my consultant work was helping one of the other analysts port software to it. One particularly irritating failure turned out to be a bug in HP's preprocessor.

I was always curious about MPE/iX but never got to play with it.