This project is in its really early 0.10 release, but I love the idea of double-clicking any DIV on a page and it opening up into a WYSIWYG wiki. Most wikis I have seen are very obtrusive, with history and stats all over the interface. It would be great to see a wiki that works somewhat behind the scenes, and only people who are interested in interacting with it know that it’s even there. Like me in the bushes behind your house 
Wikiwyg – Turn any HTML div into a wysiwyg and wikitext edit area.