We first encountered this chip when working on the spokePOV kit. We wanted to control 60 LEDs from an Attiny2313. I only had maybe 5 pins to spare so even something like ‘charlie-plexing’ wouldn’t work. A great solution came to us with the suggestion of checking out the 74HC595. This is a chip that takes serial input (3 digital pins) and has 8 digital outputs. You can chain these puppies together to have near-infinite number of outputs. Perfect for controlling LED displays!