enLIGHTen Your Mind 
This project was a partner and I's final project for CS 362 in which we had to come up with our own idea for having two Arduino microcontrollers communicate with each other.
We decided to add the twist of also including a laptop running Processing for a total of three devices in the circuit. The laptop displays a custom memory game script that we wrote.
In this circuit, one Arduino has five switches wired to it and is connected to the laptop running the memory game. The game plays a sequence of lights in a specific order that must be mirrored by the user with the switches. Upon completion of this game, the Arduino sends a winning signal to the other Arduino to initiate a victory tune on a buzzer followed by a servomotor that opens a box containing a prize.
Sample round of the Processing game running on the connected laptop.
The submission requirements for this project specified a documented writeup as shown below.
Source code can be found in the final pages of this documentation.