Ernest has done quite a lot of experiments with his collaborative editor. Early on I've advised him early on to focus on the communication/collision detetection/... part as opposed to a new really fancy editor. In the ideal world his code should be mixed in with and editor of your choice, but that is a utopian fantasy.

At the moment the demo code is focused around a special node, but Ernest is working on removing the specialisation to eventually handle any form.

If you are reading this please try it (links follow) and give him comments, ideas, etc... Don't kill him though - the learning curve of the drupal apis is steepish. Help with ideas and bug reports works better.

the drupal groups page
how to test the module page a bit outdated, but the major points still valid (hint: look for the usernames)