I recently (during a UDS lightning talk) discovered EtherPad. It’s a collaborative editor (like gobby), but uses a browser instead of a standalone application. It’s free software (Google open sourced it after buying the company that was developing it), and there’s a free online instance at ietherpad.com. Setting up a new pad is as simple as going to http://ietherpad.com/foo and clicking Create Pad. It’s written in Java, and not packaged in Debian (yet).