Although I used SunOS, Linux, and to a lesser extent FreeBSD a bit in the late 90s, it wasn't until '99 that I really got into Linux and other flavors of UNIX like AIX (while working at IBM). Compared to what I'm familiar with, A/UX is amazingly simple. You can really see how the entire UNIX ecosystem was still in flux in the late 80s. ANSI C wasn't even standardized yet. Adding bash, gcc, and less has made A/UX much more usable for me. I can't believe how much tab completion makes life easier!