fonehome allows remote access to machines behind firewalls using SSH
port forwarding.

The fonehome client is a daemon that runs on remote client machines that
are behind some firewall that you either do not control or do not want
to reconfigure, but which does allow normal outgoing TCP connections. The
clients use SSH to connect to a fonehome server to which you have direct
access. The SSH connections include reverse-forwarded TCP ports which
in turn allow you to connect back to the remote machine.

This setup is useful in situations where you have several machines
deployed in the field and want to maintain access to them from a central
operations server.