First and foremost this app is a fun game to play. It's a battle of wits against your smart phone. But how smart is your phone really? Find out.

Both players drop pieces into a box. Objective of the game is to get four pieces into a line be it horizontally vertically or diagon alley.

The game starts at level one. Each victory at the top level unlocks the next-highest level. Who unlocks the most levels?

However. There is more to it. This app is not only a fun game. It is part of an open-source project studying classical game engines. You can find the source code and further tools to study the search tree on GitHub at https://github.com/Martian01/four .