Arduino is used to make all kinds of cool projects by re-purposing things to do other cool things. Here's a novel idea which does exactly that. Schuyler Sowa turns an LED strip light into a 1-dimensional version of the classic game 'Pong'. The game is for 2 players (or a tool for 1 person to increase their reflexes), in which the 'ball' the travels down the length of the LED strip, and will bounce back if the button is pressed when either of the end 2 LEDs are illuminated.
The speed of the ball can be changed with a potentiometer, making it more difficult to hit the ball in time. In the centre of the game is a pair of 7-segment displays for keeping track of the score, and a character LCD to display other information.
The game cost just $28 to make (in 6 months), and uses an Arduino for the brain, a hacked computer keyboard for the buttons, and some clever design of the shield. Schuyler shows you all you need to know to make your own on the Instructables page.