Tiddlywiki is a wonderful, wonderful implementation of a wiki. It stacks entries one on top of another as you view them, so you can always see your history; entries can be closed when you don’t need them anymore.
When you see them stacking up, you begin to see how the information in the Wiki itself is structured; you can edit them in-place without distubring your train of thought.
The problem with Wikis is that they don’t display train-of-thought so well. Well, this one does, and I can’t wait for someone to find the killer app for it. It’s also not lost on me that it looks more like a traditional columnar weblog than most other wikis. Everyone gets weblog design; hell, everything looks like a weblog these days. Applying it to a wiki isn’t so stupid, and Tiddlywiki implements it fantastically. Who’s going to get on with the killer app, then?