Hacker News Reader

Have a look at this: http://substance.io/

I'm working on something similar: https://wikidocs.com. Although our's closed source at the moment (can't say whether or not it will remain closed), we will provide a downloadable package you can run yourself.

http://simperium.com/ is exactly what you need. It serves as a real-time data layer; you can push/pull from it from the browser, and pull/push to it from your server too.

Check out http://firepad.io, it's an open source project that uses Firebase on the backend. You could use that as a starting point and then put together your own backend.

give http://etherpad.org/ a shot