It's worth adding that the Apple II was really thefirst home computer, soon followed by others from Commodore and Radio Shack. There were other microcomputers, but they weren't aimed at a casual home market. The Apple II was the first personal computer that came "ready to use"... you just needed to connect a screen (which could be a regular Television of the time), plug it in, turn it on, and start programming it in Basic! There was no storage device included, but the Basic interpreter was in ROM, and gave you a prompt (kind of like a REPL) when you turned on the computer.
Commodore Pet: introduced in January 1977 at the Consumer Electronics Show in Chicago. What was shown had many differences from what eventually shipped, but Commodore started accepting orders. They only shipped 500 machines by the end of the year and it is hard to find out when the first ones actually went out.
Apple II: introduced on April 17, 1977 at the West Coast Computer Faire. It went on sale on June 5.
TRS-80: introduced on August 3, 1977 at a press conference at the Warwick Hotel in New York and was available for sale.
Radio Shack/Tandy and Commodore were big companies. They were later joined by Atari, Texas Instruments and eventually IBM.
The other players in the personal computing market back then were self financed (MITS, IMSAI, Ohio Scientific, Processor Technology, Cromenco, Northstar, Southwest Technical Products Corporation, Altos and so many others).
Apple stood apart as a venture capital backed startup. We later got Compaq and others but by that time none of the self financed companies were around anymore.
Apple is remembered as the number one in personal computing until the IBM PC came along. In terms of revenue that is true, but in terms of units shipped the much cheaper TRS-80 and the Pet dominated the late 1970s.
