jSave
jSave is a jQuery plugin that allows jQuery to dynamically save the current HTML, or part of the HTML either locally, overwritting the current html, or through ajax to a backend service, which can then tie into a database.
The basics will most likely come from some jQuery functions written to emulate what tiddlywiki (www.tiddlywiki.com) does. As with tiddly, the java applet may come in handy, but the overall idea is to use what is built into the browser natively.
**Update** Feb 21st, 2009. I caught wind of the subversion track of tiddly where it looks like they were implementing jQuery into the code. I also caught wind of this blog which in the details, is basically doing the same thing that is what I was looking at. I may update more on this later, but for now this project may be stalled.