Brad Newberg's AJAX MAssive Storage System (AMASS) combines flash and javascript to offer web sites a convenient, local store for large amounts of JSON data. It works only on win for now.

The AJAX MAssive Storage System (AMASS) uses a hidden flash applet to allow JavaScript AJAX applications to store an arbitrary amount of sophisticated information on the client side.

Internally, we use a hidden Flash file and Flash's SharedObject functionality to permanently store the information. We script the Flash file using it's ActiveX methods on IE and it's LiveConnect methods on Firefox. We use Flash's SharedObject's callbacks to detect when the request storage dialog is on the screen, and pass these back to the JavaScript application. We also center these values on screen.

Source: AMASS Project

This is very cool, so I won't make too much fun of why Brad put the AJAX buzzword in the project name :)