There are smaller microcontrollers than the ATtiny13. Some ARM chips will fit ... if you’re looking to break out of the world of Arduino, and you can do some pretty cool things with it, like ...

Plus, he doesn’t have an arduino. [Johannes] used very few components; 4 slightly depleted AA batteries, a super bright LED, 680 ohm resistor and a little custom code on an 8 pin ATtiny13.