EtherPad

EtherPad was originally founded by a couple of former users of Google who wanted a real-time, collaboration tool specifically for notes and documents.

EtherPad supports three web browsers—Internet Explorer, Firefox, and Safari. The tool debuted with the ability to allow multiple people to make edits to a document in real-time. A user starts by creating a document then a link to the document is generated and sent to each member of the team. After that, editing can begin.

To keep things in line and easy on the eyes, each user’s edits are highlighted in a different color. Changes are made in absolute real time, instead of after a fifteen-second cushion, like similar tools. Users can improve collaboration even further by taking advantage of versioning, and the chat functionality in the sidebar. EtherPad lets users import and export Word, PDF, Plain Text and HTML documents, or if a user wants to write a document in EtherPad, the tool now features rich text formatting, including bold, underline, italics and strikethrough commands.

Like all good Web-based tools, a free version of EtherPad is available online. However, you cannot protect your documents with a password unless you get the paid version. The EtherPad Professional Edition is free for up to three users. Above three, the price goes up to US $8 per user per month.

EtherPad is a useful tool for students, professionals and family who have to collaborate on projects. It is very practical and convenient because it does not require that all the members of the group be at the same physical location. EtherPad is also great for planning parties, reunions, conferences...Because each person's edits appear in a different color, it's easier to determine who made which contributions to the project without having to call up every member.

Reference
http://www.cmswire.com/cms/enterprise-20/etherpad-the-really-realtime-wiki-005116.php