Green your ride: Using the iPhone’s accelerometer, greenMeter’s $5.99 app displays your car’s fuel consumption as you drive. The goal is to help drivers choose efficient cruising speeds, learn how stopping and starting uses more gas, and eventually burn less fuel. When refueling, you can use apps like Gas Cubby to track mileage and see your results. At your destination, ParkMe, which tracks on- and off-street parking in major cities, can help you quickly find a spot so you don’t waste fuel circling around.