Wikipedia
Sync.in
Sync.in is a web-based collaborative real-time editor, from Cynapse. It allows multiple people to edit the same text document simultaneously. Participants can see the changes in real-time, with each author's text in their own color. A chat box in the sidebar allows participants to communicate.
Sync.in is based on EtherPad that was acquired by Google in December 2009 and released as open source later that month.
Sync.in uses the Freemium financial model. Free service requires no sign-up or registration and users can create unlimited public documents. Pro version is available in a Software as a service model and offers business-centric functions.
As of May 2013, creation of public notes has been disabled on the sync.in domain.