Aristo is the respective open source themes of SproutCore and Cappuccino, applied to their parent JavaScript libraries. You can see a great comparison of the two in this article by Allen Pike. This UI libraries duplicate the functionality of jQuery UI slightly, but look simply amazing doing so. I had already started mocking and building my own jQuery UI theme when I re-discovered the Aristo PSD. I decided to abandon my work and port the βAristoβ theme for Cappuccino over to jQuery UI.
jQuery UI