In the past we had good success with a product called Starvision.

Basically it would listen to a port for some outside transaction message
(from your pc, a Unix box or
whatever) and then route that message to a program on the HP3000. It would
then run multiple copies
of this program, and track the routing of the programs output back to the
original requestor.

Your Cobol (or whatever program) would then look at the passed message and
decide what to do,
and then send data back. Your program did all the work, the Starvision code
just kept track
of the communications part of things to simplify the applications
programming.

This middleware just did the passing of the data back and forth, along with
starting multiple processes and
keeping track of them and which message went where.

Anyone out there have experience with other products of this general kind?