[Nextdoor](https://play.google.com/store/apps/details?id=com.nextdoor) is borderline creepy but it would probably be best utilized by over-protective parents in financially well-to-do neighborhoods with young children.  It is an app that allows you setup a "private social network" with other people in your neighborhood.  You can make status updates about how terrible you think the mail-carrier is or expel other sorts of private information that you otherwise wouldn't with your neighbors.