Draftback is a Chrome extension that lets you play back any Google Doc’s revision history (for docs you can edit). It’s like going back in time to look over your own shoulder as you write.
Download it for Chrome here
Download it here
Since Draftback is a Chrome extension, your Docs data never leaves your own computer, and, unless you explicitly publish an excerpt, the extension never communicates any sensitive data with any server—it just fetches it over a secure connection from Google. All the computation for rendering the playback is done by your own computer, and it’s stored there, too.