Like Uber, but Mail
Everyone knows the Post Office is among the most inefficient, government-run programs in the world. Why not cut them out of the equation and give everyone a system to deliver mail themselves, so they can gain income and repuatation from it?
History
All credit for this amazing idea goes to SAFE Forum user "TungSvard," in this post where he explained the need. The Uber model has proven very revolutionary in breaking up the monopolistic powers of the Taxi Industry, and if we apply a more evolved version of that model to the Post Office, amazing things are bound to happen. That being said, it is unknown if any SAFE developer has taken up this project yet, despite its extreme value.
Features
The ability for any user to deliver mail, packages or even large objects to another place for payment is the main functionality of this app. Another requirement is a reputation system, to ensure people get adequately de-ranked and possibly banned from the system if they steal or snoop on the mail they are responsible for. One last possible feature--inspired by Uship.com--would allow interested mail-carriers to reverse-bid eachother down, until a price is accepted by the sender.