Roadtrip is an app that calculates the cost of driving anywhere based on your licence plate and local fuel prices. I built it with my friend Ben, and it became one of New Zealand's most downloaded apps.
Roadtrip reached #1 in the App Store with over 700,000 downloads. It solves a simple problem — knowing how much a trip will cost before you leave — and does it by pulling your car's fuel efficiency from your licence plate.