Collaborative real-time editor software
People appoint a time and log in a collab-editor session from whereever in the world. They work on a common text page. The text the different participants write have different background colors. Everything happens real-time - When you type “x” all participants see “x” with your background color exactly where you typed it within milliseconds. There are as many cursors on the page as there are participants in the session. Everybody can write whereever on the page. All see all changes being made to the page in real-time.
open-source software
proprietary software
read more on community-wiki: collaborative editor