TCPRelay is a command line utility written in java designed to relay TCP connections for servers. What does that mean? It means that you can run a server on your machine, be behind a firewall and God knows what else, and still be able to host a server (as long as outgoing connections are allowed). It requires only that you have access to another computer (called a remote relay) that does allow servers, and for that machine to have java installed.
See the website
for an example of how to run it.