The main innovation in Google Desktop version 4 is the addition of “Gadgets” — Apple and Yahoo call them “widgets.” These are little mini-applications that live within the Google sidebar and can be dragged onto the desktop. We’re talking weather apps, calculators, photos, and that type of thing — things that people want to have easily accessible all the time. The most obvious application for a marketer would be something like a countdown clock for a movie (or book) debut, a bit of free content for an online publisher, and the like. The company’s releasing an API for the Gadgets, so anyone will be able to build one, or two, or three. Kind of cool. But still requires a download, which will limit its appeal somewhat.