Etherpad is an online word processor with formatting options.
It offers a lot of the same features as Google Docs, but is not suited for sensitive information as it has limited password protection and access control features. It does have lots of other great features, however. Edits by different authors are colour coded, and there is a chat window which allows you to talk in real time to other people working on the same document. You can undo and redo changes easily, and import/export as text, HTML, PDF and other common formats.
There are many different installations of Etherpad listed on etherpad.org. We recommend pad.riseup.net as it has https support, which makes it more secure.
Collaborating quickly on a public text
Taking notes of online meetings collaboratively, in real time
Quick and easy to use; many output formats
Not many security features, although there is a secure VPN and Tor port through riseup: http://pad.riseup.net