Sage on HP-UX
Sage officially supports several different linux distributions and Apple's OS X. Sun's Solaris will be supported very soon. There are no official plans to support HP-UX, but some attempts have been made at building Sage on HP-UX. Where problems were found, fixes have been incorporated. For example
are all bugs affecting HP-UX, which have been fixed.
http://trac.sagemath.org/sage_trac/ticket/7505
makes tests for certain compilers, including that of HP's compiler on HP-UX.
So whilst HP-UX is not a high priority, some work is being done. If you would like to contribute HP-UX patches, then please do so.