Saw a mention of this wiki on kottke.org. It's really quite nifty, and all fits in one file. The author notes that there is no server side for it, and I had the idea of helping out by writing one. Unfortunately, this would break the all-in-one-file aspect that is part of why this is so neat. Or does it? Couldn't you just embed some PHP code and use remote scripting to have the wiki page send the content in a POST form to itself, which then uses PHP to merge the new content into the wiki and overwrite the file. Weird, but a fun concept. I suppose you could really do just about anything in one page, if you were determined. But the tiddlywiki does it all in a single page _view_ too. Which is really surprisingly enjoyable to use.

Take a look at a sample (broken) implementation.