I've used TiddlyWiki in the past with things like the documentation for my ASAV Gateway that I've given in talks and presentations. However, I don't think I was ever really using it effectively before now.

In case you don't know, TiddlyWiki is this handy-dandy little Wiki that is entirely self-contained in a single HTML file. All of the Wiki-functionality it has is handled client side in your browser instead of server-side. This means that (unless you set up some complicated authentication system via web interface) all of your Wiki changes will be local only.

On the surface, this may not seem very useful, but that's only until you alter your perception of what a Wiki can be used for.