Free Simple Collaborative Tool for Sharing Documents
Entri is a free collaborative tool for writing and sharing documents. Say you are writing an article for your blog and you want to share with your readers before you publish it to get feedback and allow changes.
They are building the API, they will have a feature that will let you flip between past Entris that you made, plus a new text editor with better formatting features. You will be able to integrate blogging engines such as WordPress and Expression Engine as well.