Kai's Function Box is based on a function guessing game that we often play verbally in our family.
The rules are simple: The function creator comes up with a function such as "x + 1". The guesser gives an input such as "5" and the creator responds "6". The guesser tries to figure out what the function is based on the creator's responses.
This app-ified version of the game allows you to limit the complexity of functions so your friend doesn't give you a 10 step function :-) You can play against your iPad at five difficulty levels ranging from easy (simple addition and subtraction) to crazy, which produces multistep functions with exponents, roots, etc.
Feedback is always welcome. We hope you enjoy the app!