Google developed an Android social network for parking spots called "Open Spot," which tells people who're leaving parking spots share their spots with people who're searching for parking. "Open Spot will show you parking spots located within a ~1.5 kilometer (km) / ~.9 mile (mi) radius of your location. As you move, Open Spot will automatically refresh to show you parking spots within a ~1.5 km / ~.9 radius of where you currently are."
Spots are removed from the map after 20 minutes. In the map "Red pins are freshly-marked spots, Orange pins are spots marked over 5 minutes ago, and Yellow pins are spots marked over 10 minutes ago," explains Google.
Users gain (parking) Karma points for their participation. And, who might try to fool the system and frustrate others are called "griefers" —Google says we're watching for behavior that looks like a griefer spoofing parking spots. We've a couple of mechanisms available to make sure someone can't leave a bunch of fake parking spots. If we see this happening we'll take steps to fix it."
More Info: Open Spot