Financial software specialists Kylom have produced what looks to be one of the most innovative 7650 apps available. Its a calculator that is specially designed to allow easy input using the 7650 joystick.

From http://www.kylom.com

Your joypad operated smartphone needs a joypad operated smart calculator. Here you have it: unless you have a Bluetooth dongle plugged in your brains, you will not be able to make calculations on your Nokia 7650 with less thumb efforts than with JoyCalc. Thanks to its diamond shaped virtual keyboard, you can select and actuate each function key with 2 actions on the joystick only, in "full" display mode (left), or in one single move, in "basic" mode (right):

JoyCalc can also be operated with the device's keypad closed. Use the corresponding menu option, and you will select numbers in the same way as operators (2 moves for each digit):

Last but not least, JoyCalc can be operated either in standard mode or in RPN (Reverse Polish Notation) mode, with a 3 level stack: