You could put the Arduino in deep sleep, if you wanted to and that LED will still blink. With a little work, you could probably adapt this idea to any number of circuits out of the 555 playbook ...

Controlling 64 LEDs over a three-wire interface ... To actually power and control the entire circuit, [Martyn] used an Arduino loaded up with a program based LedControl library makes ...

This project aims to create an adaptive musical instrument that allows physically challenged individuals to express their ...