The app I used was "gas cubby" recommended by a friend to keep track of my car. You could record your fillups and compute gas mileage and lots of other statistics. You could keep track of the vin, the insurance policy number, part numbers and service intervals.

I slowly put all my data into it and...

The app was sold, and one day they changed it and uploaded all my data to the cloud.

I deleted the app (and apparently all my data). what jerks.