TripLog automatically tracks your business mileage using the GPS in your smartphone.
Just set up your vehicle, take a few seconds to create a new trip, and drive! When you hit your destination, just tap End Trip.
TripLog can also calculate fuel economy, manage multiple vehicles and business entities, and support commercial trucks.
The app can even email you IRS compliant mileage reports in CSV or HTML format.
TripLog is not only free, it's also ad free!