It used to be said [...] that AIX looks like one space alien discovered Unix, and described it to another different space alien who then implemented AIX. But their universal translators were broken and they'd had to gesture a lot.
-- Paul Tomblin
Although I suppose that if you held a gun to my head and forced me to select a commercial Unix for a project, and if my stunned perplexity didn't get me killed, HPUX would be an admirable choice.
It is a shame. Many challenges we find today happen to have been solved in the 60s. Then in the 70s, then in the 80s...
EDIT: One thing that I love is the fact that they distributed apps in intermediate form and then compiled at installation time. (Sounds familiar, right?)
There were import libraries and symbols to be exported needed to be defined in export files.
Of course, eventually they converged into the standard UNIX model for shared objects.