Cale's magic numbers is a math based computer game 100% conceived of by my 7 year old son. I was so proud of him for thinking up the rules of the game by himself that I created a web based version. You can play the game @ http://cannuk.github.io/cales-magic-numbers.
The goal of the game is to earn exactly 20 points. To do this you open envelopes and either add or subtract the number inside the envelope from your total points. Once you reach exactly 20, you win! The game relies on you to do the addition and subtraction. There is no penalty for a wrong answer. Just keep trying until you get it correct.
Cale's Magic Numbers was built using Backbone, and Marionette.