pbnc runs in userland and acts as a simple TCP port forwarder.
It  has  a  single-threaded design  (uses  select(),  does not
fork). It can handle multiple targets with an unlimited number
of clients (at least in theory), and supports simple  IP-based
access control. Since pbnc works on network level, it does not
care  about  the  application  protocol.  It  can  tunnel  FTP
(control connection), SSH, HTTP and all other protocols  using
TCP  communication.  Application-level  SSL/TLS  encryption is
also no problem.

WWW: http://duncanthrax.net/pbnc/
WWW: http://freshmeat.net/projects/pbnc/