Digispark USB Mood Lamp that Sleeps When the Computer Does.
I wanted an LED mood lamp that's only on when my computer is awake. The DigiSpark and its LED shield was perfect! http://digistump.com/wiki/digispark/tutorials/rgb
With a full USB connection, the host sents frame pulses to the devices. The Digispark counts these and when it sees they're not being updated it fades away until it sees frame pulses again.
See it in action: