Review our UI mockup tool, ScreenSketcher
pistoriusp: I'm on a Mac, so I can't review your application. Most of the developers that I know are on *nix/ OS X. We're in different circles; I'm sure you'll have clients.I don't really see why a person would want to use a desktop application instead of a web based application like Balsamiq. I honestly believe that the next step to improving Balsamiq would be to stop using Flash.(Edited to provide more clarification than just: "I'm on a mac.")