Use your phone's camera to capture a picture of your maths problem and this app will show you how to solve the problem. Price: free. Device: IPhone, IPad, Android
The Calculator | Download for iOS
Apple's free calculator. Use in the vertical position for a basic calculator, tip your phone on the side and you will then be able to use it as a more advanced scientific calculator. Price: free. Device: iPhone, iPad
RealCalc | Download for Android
A realistic scientific calculator for Android. Android's #1 Scientific Calculator. RealCalc is easy to use, but has full help included in the app. Price: free. Device: Android.