Go to TiddlyWiki. Bounce around the site for a bit and enjoy its interesting user interface. So far, just another wiki implementation.

Now, save that page you’re playing with as a local HTML file. Close your browser window. Open the file. Note that it’s exactly the same. Whole thing is self-contained within your browser.

Reattach lower jaw to head.

The one thing that makes this less than orgasmic (well, if you’re as into information tools as I am) is its horribly painful save method (which the author apologises for), and the charming feature that since your browser won’t recognize a changed page, it’s all too easy to close the window and lose everything you’ve worked on. But still… wow.