HP-UX and IRIX (SGI) are on a "slow retirement" plan. The number
of users is decreasing regularly and eventually I expect that we may
stop supporting these systems, although it depends entirely on demand.
For some types of licenses, we charge more for these two systems than
for other unix systems.

This being said, HP-UX does power the largest unix LISTSERV site in
the world (by number of subscribers), which is the second largest if
you ignore operating systems. LISTSERV works very reliably under
HP-UX. We ran into all kinds of annoying HP-UX specific problems,
but they have been solved years ago and now the product is very
stable. There is no technical reason to avoid HP-UX, it's just that it
is losing market share rapidly (at least for LISTSERV).

  Eric