As promised,
we hereby release all the source code to EtherPad.

http://code.google.com/p/etherpad/

Our goal with this release is to let the world run their own
etherpad servers so that the functionality can live on even after we
shut down etherpad.com.

If you are just interested in running an etherpad server, these
instructions should get you up and running.

Running EtherPad behind a firewall is rather intriguing. Might have to do some experimentation.