1976: COSMAC ELF
In august 1976 issue of Popular Electronics magazine (USA), Joseph Weisbecker published a design for "Low-cost experimenter's microcomputer" using RCA's COSMAC CDP1802 microprocessor chip. It is a very simple computer having 256 bytes (yes, bytes) of memory, switches as input and LED as output. No ROM, every time you turn it on you have to enter program to RAM by toggling 8 switches, one for each bit. After the switches are set, pressing IN-button stores that byte to memory and increments address. Remember, that it only had 256 bytes of RAM, so it was not that big deal, but still takes some time. There is no way to step address backwards - if you made a mistake you have to start from beginning.
COSMAC ELF became a hit among hobbyists in the USA. It was simple to build by almost anyone and the components didn't cost much.
Later more designs based on ELF were appearing like Netronics ELF II and Quest Super-ELF.
...and the control logic. That's all!
There was also a video circuit using 1861 "Pixie" chip. It needed only a few components and provided a video signal.
Copy of the original article can be found at least from here.