I was using Ultrix as late as 1997 on an old DECstation at school. I remember crashing it by clicking on the 'clear' button in the graphical login program, and getting root (after we (the students who were the de-facto admins) lost the password) by pressing Ctrl-C at bootup. It had a funky directory structure; among other things it kept home directories in /u/usr/. Ultrix wasn't as bad as some people make it out to be.