PiratePad is a web-based collaborative writing tool, much like Google Docs. However, PiratePad doesn’t require a google account to use. I think too often we turn to Google for a collaborative writing space without considering the myriad of reasons some folks may not (choose to) have a google account (privacy, age, access speed, etc.). PiratePad offers a free, robust, open-access alternative.
A few of PiratePad’s unique features are the availability of multiple languages (hundreds!), the option to choose a license (including Creative Commons), and a “time slider” that allows the play back of revisions.