Port funnels?

["Stout, Bill" <StoutB () pioneer-standard com>]

I'm looking for a server utility that would funnel application ports onto
one port number pair.  Any exist?  This would greatly simplify remote access
to applications.

I'm rather unclear on why application vendors do only define the inbound
port, and then use random (or simply different) ports to reply.  I may have
missed that day of lecture.

Bill Stout