Navigation system uses crowdsourcing for route guidance

Waze is a free navigation application for GPS-enabled phones that uses data from users to generate turn-by-turn routes and provide other information such as traffic conditions, faulty traffic lights, and accidents. I just downloaded it for my iPhone.
Waze What's most interesting about Waze is how it uses the power of the crowd to build its map database. Just by driving along with the application open, users are contributing data to Waze. Although this does make the service somewhat dependent on building critical mass in order to be successful, the company is confident they can do so. That's because Waze originally launched in Israel and in less than a year's time, they already have 91% of the country mapped. Here in the U.S., that process will obviously take longer, but Waze believes they'll have at least one metropolitan area completed in the next three months - the San Francisco Bay area, of course.

Waze: Free Turn-by-Turn Directions for Mobile Users