A Phone app that allows you to type in the total amount to be paid, and it generates a bar code for the register to scan.
Car horns that gives an electric shock if pressed for more than 3 seconds in the city traffic.
Integrate exercise equipment two-way with tv console / computer for scenic routes worldwide (film vs game) with speed / resistance response
Have cities give abandoned and unused property to artists as workspace under the condition they create something visually striking with it.
A website where people can advertise available parking spaces in their houses or buildings.