That's the idea behind Google's new Open Spot app. When you're leaving a parking space in the city, you can use Open Spot to record its location on a map. Fellow Open Spot users looking for parking can then look up recently vacated spaces in their area. The freshest spots show up as red pins; older ones show up as orange or yellow pins. To encourage people to get in the spirit of pay-it-forward information sharing, Open Spot rewards frequent users with "karma points." For now, the app is available in the United States, Canada, and, oddly, the Netherlands, for phones that run Android 2.0 or higher.