CarMap
A route planner for drivers: it works out fuel use at a given speed, fuel cost, vignettes and road tolls.
It starts with your car: you enter tank size, fuel consumption, power and fuel type, and the entries are saved through an API into a shared database. Then you pick a route and a speed, and the calculator works out consumption from the curve of that particular car, because 140 km/h burns fuel very differently from 70. The map shows range circles for one, two and three tanks, refuelling points along the way and places worth stopping at, pulled from Google Places. At the end you get a cost breakdown: fuel, vignettes, tolls and the full return trip, shareable with a link.
Your project could be next.
Tell me in two sentences what you want to build. You get a quote within 48h.