Steve Rubel over on Micropersuasion credits Simon Shandler for finding what looks like a Google real estate app. This link takes you to a very rough version of a New York City real estate map. The listings are fictitious and the labels are incomplete but the site does look like someone has been playing with it. The page is built using the Google Maps API and mashes up data from Google Base. I've also stumbled across one that resembles a job search app as well. Stay tuned!