iPhone/iPad: If you dabble in electronics tinkering with the likes of Arduino or you enjoy popping open your electronics and poking at them, Circuit Playground is an app that offers quick reference to decipher between components and make calculations.
Created by the electronics store Adafruit Industries, Circuit Playground works as a simple reference manual for all your electronic tinkering. It has a guide to deciphering colour codes on capacitors and resistors, a number of different calculators for different equations, and the ability to quickly convert between decimal, binary and hexadecimal. It's not going to be everyone's cup of tea, but if you hack electronics, it's a powerful resource. Circuit Playground is $2.99 in the iTunes App Store.