TitanPad is a real-time text editor that allows multiple people to edit a document simultaneously. The content in TitanPad pads can be exported as a HTML, PDF, Word or plain text files (among others). It has automatic saved revisions and has a cool “Time Slider” feature that lets you play back all of the content that has been added or modified. You can even set up a private pad that is password protected.
Check it out here: http://titanpad.com/