I have started using TiddlyWiki as my knowledge management tool.
It is all based around little packets of information referred to as Tiddlers. These have a title, some text, and can have several tags. There is also a long list of special syntax for adding functionality and for formatting.
There seems to be many people using it for a variety of purposes. However, the information about TiddlyWiki and how to use it is pretty limited. I have perservered and now have it up and running very efficiently.
At some point, I will post my tips on using TiddlyWiki including the list of syntax I have discovered and some quick pointers on implementing themes and macros. I will also give you my guide for locking down TiddlyWiki so you can publish your wiki on the web in a tamper-proof state.