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What makes TiddlyWiki great for such a purpose is that it's just a single file. Within the file are all the Javascript, CSS, and HTML you need to maintain a Wiki. You can move the file around and it will contain all the stuff you've written.
Out of the box, TiddlyWiki looks simple to use. If you've used a wiki in any form before, you can get the hang of it pretty quickly. If not, there are several tutorials out there. Being somewhat obsessive-compulsive, it took me a while to customize it to my tastes; that, unfortunately, was a little harder to figure out, but became easier as I got the hang of it.
The default TiddlyWiki installation is a little basic, so I've had to spruce mine up with a couple of plugins. I installed a theme from TiddlyThemes, the ForEachTiddler plugin from abegoExtensions, and the Calendar plugin from TiddlyTools.