ssh -L 8080:localhost:80 [ssh addr]
then you can access remote http:80 via http://localhost:8080/
access service on another machine that is blocked via missing port forwarding or iptables
[Internet-inaccessible machine] ssh -R 55555:localhost:22 [user]@[your public host]
[your public host] ssh [Internet-inaccessible machine's user]@localhost -p 55555
Ability to ssh into remote server that is not accessible via Internet