NEXTSTEP 3.3 should FLY on that sucker, assuming you can get install media. Here's a source for a complete (now free, but only as in beer, not as in speech) office suite for NEXTSTEP and OPENSTEP: http://download.ithinksw.com/lighthouse/

Note that I don't know if the binaries there will run on the PA-RISC version, but if they do, you should have a productive little box...