Here are mine
ProcalcApp -only calculator on the app store that can handle complex numbers (developed by a guy who I was in class with)
MyFitnessPal-the reason why I weigh 30 Kg less .
- Electrodroid Ridiculously useful when you have to design and build electric circuits. Especially the resistance combination calculator.
Put in desired resistance and it calculates a serial or parallel combination of standard resistors that match your desired resistance as close as possible.
Wolfram Alpha Useful for getting tide-tables, signal generation, in fact just basically the computer from Star Trek. Not bad for R36.