The coolest wiki ever since sliced bread. In fact that may inspire me to create a new category “Sliced Bread” – just for cool and useful stuff I find.
Tiddlywiki is an entire wiki coded in a single 200k HTML file. This means you can simply download their empty.html to your local disk (and change the name – mywiki.html). Open that fine in your modern browser. Play with it. It’s an entire wiki system – in one file, on your hard disk. You can edit it, add sections, html links, wikilinks, change a bunch of settings, and such. Very useful as a mini-notepad that you can use anywhere you have a browser. Almost as good as a magical yellow sticky application that would actually keep all your notes handy when you need them, but out of the way otherwise.