gobby may not be the best editor out there, but as far as I know it's goal was to be a testbed/implementation of the obby (now infinote [1]) collaborative editing protocol. The underlying library is quite easy to use and integrate into existing editors, for example I once implemented a gedit plugin [2] which used libinfinity to add collaborative editing to gedit although it has since gone stale.
[1]: http://infinote.org/ [2]: https://www.youtube.com/watch?v=rXzI2dInXKI