I've been trying to find a Wiki that could run with as little set up needed, and was as standalone as possible. TiddlyWiki is a small, lightweight wiki that doesn't require anything beside a web browser. It can be edited just by double clicking an entry. A basic setup runs from only one file. One small, less than 500KB file that can serve as a personal Wiki/notebook/journal. I should mention it can embed media and can make an external(local) RSS feed. The RSS feed may up the file count, but only by one(for those of you that failed every math class you ever had, that makes 2). In addition to this and the startup parameters, it has a slew of other features that are even better. There is also links to other Wikis and server side options as well. Just click the link "Download Software" on the left to aquire your own.
If you're a Pen and Paper RPG fan you might be ineterested in a modification of GTD TiddlyWiki. "TenFootWiki 2.0 a personal campaign notebook for roleplaying gamemasters". It looks a little more polished and shows some more features of the original Tiddly from which it was based. A copy of this can be found in the about entry under the "Get Started" heading.