Google Docs - is a free, Web-based word processor, spreadsheet, presentation, and form application offered by Google. It allows users to create and edit documents online while collaborating in real-time with other users.
EtherPad - EtherPad lets multiple people work on the same text simultaneously.
SynchroEdit - SynchroEdit is a browser-based simultaneous multiuser editor, a form of same-time, different-place groupware. It allows multiple users to edit a single web-based document at the same time, and it continuously synchronizes all changes so that users always have the same version.
Dabbleboard - Dabbleboard is an online collaboration application that’s centered around the whiteboard.
Twiddla - Twiddla is a real-time online collaboration tool. Its beauty is in its simplicity and accessibility: no plug-ins or downloads, no need to work around complex firewalls, no advanced scheduling.
Gobby - This one's for Collaborative Programming! Gobby is a free collaborative editor supporting multiple documents in one session and a multi-user chat. It runs on Microsoft Windows, Mac OS X, Linux and other Unix-like platforms.
CoWord - This is for our very own Word! CoWord converts MS Word into a real-time multi-user collaborative word processor. With CoWord, you and your collaborators can edit the same MS Word document at anytime (the same time or different times) over the Internet. Changes made to the document are immediately displayed for all users to see.
PLUTEXT (docx4all) - Create, edit and collaborate around docx on Windows, Linux and OSX. You can work on a document at the same time as other people.
Zoho - The Zoho Office Suite is a Web-based online office suite containing word processing, spreadsheets, presentations, databases, note-taking, wikis, CRM, project management, invoicing and other applications developed by AdventNet Inc., an Indian-based company.