FlightCaster predicts flight delays, often hours before the airlines. From the developer page: "The FlightCaster API is primarily used for retrieving information about the likelihood that a flight will be on time. Although other information is available as well, such as general airport information, general airline information, general weather station data, METARs, and TAFs."
Have you had to pick someone up from the airport only to end-up doing several laps of the airport because the flight was late? This sort of setback due to arrival delays is one of those modern day inconveniences that FlightCaster and their FlightCaster API hope to eliminate.