Waze is a free GPS application that does all of the normal GPS navigation but Waze sends back real-time data about your transit speed to update advice to other users.
So – if multiple users heading down a road are travelling much slower than usual then that road will get a red flag alerting people that they should consider alternative routes.
As of January 2012, the app has been downloaded 12 million times worldwide. Currently Waze has a complete base map in the United States, Canada, United Kingdom, France, Germany, Italy, Netherlands, Belgium, Israel (claimed to be the best map for that country, South Africa, Ecuador, Argentina, and Panama.
This is clever stuff – you can see obvious extensions to crowd-sourced public transit information and the like. We opt in to share our data for the greater good.
See www.waze.com for more info.