Rui CarmoTempura is a Wiki (or anti-Wiki) concept I've started contemplating recently, as I start relying more and more on IMAP for all sorts of things.
Imagine, if you will, a Wiki-like site that is a crunchy shell around an IMAP server (or a maildir, or a set of mbox files) for storage, and which relies completely on the HTML portions of "mail" messages, using hyperlinks defined in them for navigation.
Yes, this means zero markup hassles, attachment support, and painless insertion of images into posts (it would only depend on how clever your MUA is, since parsing MIME and rendering it as HTML is pretty straightforward).
Like Yaki, Sushi and Sashimi, this could leverage server-side caching to minimize the hassle of accessing the IMAP store and rendering the RFC:2822 storage to HTML, and it would also play nice with my Data For The Ages approach, allow for easy secure remote editing, let you delegate whole subtrees (via IMAP shared folders) to other people, etc., etc.