Quantity   Component name
1 × Raspberry Pi Any model will do, A+ will be slower.
3 × Big Pushbuttons Little ones work to, but are not as fun to press. Get them at Sparkfun or Adafruit.
3 × Transistors The leds in the buttons draw too much for the Pi, so use transistors. I used an H-Bridge
4 × IDC Connectors (Female) Crimp these with ribbon cable to connect the buttons/leds together.
4 × IDC Connectors (Male) Solder on wires to connect to Pi or buttons.
1 × Ribbon Cable To connect the buttons together
3 × Case One for each button, to house the wiring. I made mine out of plywood, but 3D printing would also work.