HP/UX is a common misspelling of HP-UX. MPE admins almost always spell it HP/UX. People who don't know what it is almost always spell it HPUX.
HP-UX is a marvelously stable OS that runs on fairly decent hardware. It comes with a hideously crappy admin "tool" called SAM and a freaking wonderful version of LVM.
Anyone declaring that free *nix rules and commercial *nix sucks, has never used Online JFS and LVM.