Etherpad is an online collaborative editor that tracks every keystroke you type. Paul Graham wrote an essay using Etherpad, and now you can see him writing it. It’s as if you’re looking over his shoulder, giving you a glimpse into his writing process. (Hint: it includes liberal use of the backspace)
The playback feature isn’t generally available for Etherpad yet, but from what I understand the keystrokes are being tracked and the playback feature will be available for existing documents later on.