This is an amazing series for understanding how you can make some sand 'think'. It's not just about putting it together - it's his way of explaining why and how things work that makes it an incredible watch.
I built a modified ALU desk display from watching this - you use dip switches to set the value (between 0 and 255) and it will the count up in that number, displaying the decimal result in a 7 segment display (and binary as leds). It can count down too!