From book to app
The B737 Performance Reference Handbook originally saw light as a hardcopy book but is now available as an iPad/iPhone app. It is an electronic reference guide for professional airline pilots flying the Boeing 737, but it is also very useful for pilots of other large civil twin-jets, airline dispatchers and trainees.
Maurits Hulshof
The app is written by an airline pilot with an aeronautical engineering degree who is an active captain/TRI on the Boeing 737NG.
It explains all relevant performance matters which you come across in your operational life as a pilot, from dispatch until the final landing.
Alongside the 737 Management Reference Guides
Pat Boone's 737 Management Reference Guides are an operational reference which many 737 crews already carry. The B737 PRH is complementary to it: the MRG covers the operational procedures, this app explains the performance behind them.
Both are useful to have available on your iPad.