This module integrates Drupal 7 WYSIWYG module and the open source collaborative editor Etherpad-Lite.
Please make sure to follow the instructions in the README.txt.
To enable several users editing a node in the same time you should use the Local Editable formatter for the text fields i.e. go to the Manage Display tab on your
content type (e.g. ?q=admin/structure/types/manage/article/display) and choose
Local Editable for the text field you want to have etherpad-lite enabled.
There is a alpha-level attempt of Drupal 6.x integration with the classical Etherpad but it is not maintained. You can give it a try by accessing https://github.com/KyleAMathews/drupal-etherpad.