Google Docs, Zoho Writer, and other online word processing services are great tools for collaboratively writing with others. But to use those programs everyone you want to collaborate with needs to have an account and you need to have their email addresses or account names. To eliminate those steps and get collaborating faster, try one of these three registration-free tools for collaborative writing.
http://www.freetech4teachers.com/2010/09/3-registration-free-tools-for.html