From the tcpcat README:

Tcpcat is a simple program that is like `cat' but it works over TCP streams
to allow you to cat from one host to another.

The host common way to use this program whould be something like this:
on host a: $ tcpcat -l 93255 | gzip -dc | tar xvf -
on host b: $ tcpcat -h hosta:93255  file.tar.gz

Another good use for this program is debugging network stuff. When debugging
a newtork client or server you can pipe the output of tcpcat to a hex dump
(I recomend xxd which comes with vim). Also it can act as a crude telnet server
when invoded with --listen, --input, and --output, this mode is quite useful
for network program debugging as well.