I just took a look at a demo video on your site - I'm just guessing based on appearances, but are you using CKEditor for your base editor, and then popping up a new window using the lite plugin to show tracked changes?
If so, we're using the same toolkit... but if not, I'd love to know if you found a better track changes project via open source, or if you rolled your own. The lite plugin works OK, but not well enough for some of our more legal-focused clientele, so I'm scoping out other options.