Tiddly But Cool

TiddlyWiki is a fantastic little toy. It presents an entire Wiki in a single HTML file. No webserver, no database, just a single HTML file.

A whole heap of CSS/Javascript magic goes on behind the scenes to save any edits back to the orginal HTML file, making it eminently portable. You can drop this thing on a USB token and carry around a self contained notebook that you can update using whatever computing you happen to have access to.