TiddlyWiki
I keep an eye out for new ideas in Wiki technology (see my post from February Looking at Wiki), and I recently became fascinated by TiddlyWiki. It is sort of a one-page client-only Wiki written completely in Javascript and HTML. Like my EditThisPagePHP, it appears to be an elegant experiment to look into the future of this medium of user-editable content.
The key feature of TiddlyWiki is that instead of WikiName links leading to new pages, it displays a new set of microcontent at the top of the current page, pushing your previous content toward the bottom of the page.