OK, so it’s not the smallest computer ever, but at only 3mm long it is the smallest computer I’ve ever programmed. This is the PIC10F206 and yes, that’s the tip of my finger it is sitting on.
This little beastie has less than 1k of memory and only runs about as fast as an Atari ST but hey, it’s a real honest-to-god computer and if you only want something simple done, it can be real useful. Oh, and it only costs 70 cents, way cheaper than the Atari.
So what did I use it for I hear you ask? well, I just needed a 40kHz oscillator with some low frequency modulation to make an ultrasonic insect repeller. You could probably do that with a couple of CMOS chips and a ceramic resonator but this solution is cheaper, smaller, uses no external components and I even have a couple of spare I/Os left over to, I don’t know, flash a light or something.