Gigatron, TTL computer kit without a CPU

Provenance: There was a recent post about PiDP-11 which is awesome in itself, but the page led to this which is probably more remarkable than is apparent at first; a Single Board Computer which implements all logic in TTL and with a remarkable functionality given the relatively few chips.

There are many SBCs of the era using more chips that this, despite having a Z-80 or 6502 onboard.

You can build them with 74xx, 74LSxx as well as 74HCTxx, or mix those. Mixing with 74HC is also possible if you're careful, but full 74HC won't work.