Here's an app that is intended for carpenters, engineers, designers, handymen, and cooks...but...it wouldn't be a bad app for some students too. Quickly add fractions so you can stop using your tape measure as a slide rule. The keypad is set up like a fraction. A set of numbers 0-9 on the left as whole numbers, a second keypad of numbers in the top right for the numerator and a third keypad in the bottom right of the screen for your denominator.
Click in the fraction and add, subtract, multiply, or divide with a second fraction and your answer is spit out in both fraction (in its simplest form) and decimal form!