I would like an app that would report abandoned (possibly stolen) vehicles in a neighborhood and allow owners to possibly track down their car.
I know someone whose car was stolen in the middle of the night from in front of his house. It was found by the police by morning but the thieves had already stripped it and stolen everything from inside of it, even the battery and some parts. They left the vehicle to be picked apart by petty thieves. The place where it was found was a "car graveyard" according to a neighbor. She saw Hondas abandoned there on a regular basis. The data about where these vehicles are often found could be used and supplemented by neighborhood watch groups or citizens that could report abandoned cars or suspicious activity, and those who are missing a vehicle could get more information about where their car might be.
Parts from these cars or stolen items could also be tracked and searched for online.