Check out Daryll Strauss’s Digital Dominos:

I revealed the Digital Domino at the CrashSpace booth at MakerFaire this year. It’s a small electronics kit that allows users to line up virtual dominoes and knock them over by pressing a button. Each domino lights up an LED and uses an IR pulse to knock over the next one. They can also be looped to repeat the pulses. We won an editor’s choice award at MakerFaire for them.

These were designed to be very easy to hack. The timing can be changed, the lights can be changed, they can be used to trigger other devices, they can be triggered by a microcontroller, they can sound a buzzer, etc.