jc

The history expansion character (! by default in bash) can do lots of cool things:

http://www.thegeekstuff.com/2011/08/bash-history-expansion/
Formal reference:
http://www.gnu.org/software/bash/manual/bashref.html#History-Interaction

Useful tool in many scenarios I imagine, but it's worth noting that while using any server that will let you bind to 0.0.0.0 you can simply set up forwarding rules on your router/firewall and anyone outside your network should be able to reach it. WEBrick does this by default.