TiddlyWiki. It's an incredible DHTML technology developed by some guy named Jeremy Ruston. He tries to describe it as a non-linear personal blog.
That's not to say it's without limitations. For example, it's best suited for textual information because, although you can include images in a TiddlyWiki, you don't have quite the control over the images as you would in a standard Web page. Additionally, since all the content is stored in one file, if the Web page has a large volume of content, it could take a while to download the page after it's requested.
That said, it's potential for a Web "site" is amazing! In fact, probably one of the best examples I've seen of Web user interface design is a TiddlyWiki page. Elise Springer, a philospher at Wesleyan University in Connecticut, USA, is using TiddlyWiki for her homepage. You can check it out at http://espringer.web.wesleyan.edu/. MyWiki is also a TiddlyWiki page. It's not nearly as impressive as Elise's, but if you're so inclined, you can check it out at www.wardconsulting.com/wiki.