http://www.tiddlywiki.com/

It's a completely standalone wiki ina single HTML file. It performs this magic by embedding javascript directly into the file, which provides all the functionality.

Ok so this approach has it's limitations, but think about it. A single HTML file. You don't even need a server or database, just open it up in any browser and off you go. There are a number of sites powered by it, and an active macro and plugin development comunity.