socat is a relay for bidirectional data transfer between two independent
data channels. Each of these data channels may be a file, pipe, device
(terminal or modem etc.), socket (UNIX, IP4, IP6 - raw, UDP, TCP), a file
descriptor (stdin etc.), a program, or an arbitrary combination of two of
these.

socat can be used, e.g., as TCP relay (one-shot or daemon), as an external
socksifier, for attacking weak firewalls, as a shell interface to UNIX
sockets, IP6 relay, for redirecting TCP oriented programs like brutus to a
serial line, or to establish a relatively secure environment (su and chroot)
for running client or server shell scripts with network connections.

WWW: http://www.dest-unreach.org/socat/