Very nice. What happens when two clients open the same document library at the same time? Do they only overwrite content if you add comments etc?

We created a web based multiuser web annotation and discussion system, for inline annotations around ‘99-00, then the dotcom bubble burst and we had to shut down. I have been looking for something along those lines since then. There have been several attempts by others but it seems that the alternatives (PDF, screenshots, email etc) are hard to displace.