i had an idea for an app called "Balls in My Pocket". it helps you know how many tennis balls are in your pocket at any given time. don't steal my idea.
i do think that i'd love a tennis app that i can use as a coach and/or spectator to track match stats. for example how many winners and errors a player had in a set. and on what wing and what location on the court. number of aces and double faults too. the key would be to make the input of that information quick and easy and then display all that information.