Belmondo is a 'create your own book' site that comes with pre-defined books for the most common situations. They have guestbooks, sisterbooks, and others. And if none of them fit your needs, create your own.
While there's plenty of other sites that also do this, Belmondo makes it possible to do this together with others. It allows for multiple editors to work together in the same book, at the same time.
For this client I've rebuilt their Magento piece by piece after they moved away from their previous partner. After that we rebuilt the editor they use for their books from flash to a html5 version. We also implemented a system that creates the necessary images for a book before sending it off to a printer.