Writeboard

Writeboard is a shareable, web-based text document that let you save every edit, roll back to any version, and easily compare changes.  You can use Writeboard in a solo effort or in a collaborative effort.  For each Writeboard you provide a name, a password, and your email address.

When you write something you can share it, revise it, compare it, and then store it in a virtual backpack to help keep them organized.  The software allows you to click various versions via a check-box and then you are able to make comparison between the versions and see what has changed.  You can subscribe to a document's RSS feed so that you can be notified when changes are made.