This reminds me of my Gakken GMC-4. It's a 4-bit computer like this, but a physical piece of hardware. It has 7 LEDs, one 7-segment LED, a 20-key keypad and a tone generator. You have to key in the programs manually on the keypad, but you've only got about 100 4-bit words into which to fit your code and data. It's further constrained by the fact you can only directly address 16 of them for data. Even so, it's surprisingly fun and challenging to write little assembly programs for.