Atari 400
(prolly not until late 1980 that i was using it though)
http://www.laughton.com/paul/abps/oss/two_births.html
"I don't know exactly when the concept of the Atari Computer was developed within the corporate mind of Atari, Inc., nor do I know all of the people responsible for nursing that concept into reality. The following history covers the relationship with Atari, Inc., during the evolution of the system software.
Sometime in early 1978, when the Atari 800 and 400 were still called "Coleen" and "Candy" and were still in the breadboard stages, Atari bought a copy of the source for Microsoft 8K BASIC. This version of BASIC was fundamentally the same product that was implemented by Commodore in the early PETs, was used by OSI, and was a close ancestor of Microsoft's Applesoft Basic. Six months and many, many Atari man-hours later, that 8K BASIC was almost functioning properly on the Atari prototypes. But buying source for a program buys you just that: source. Generally, you also receive little documentation, sometimes obscure code, no guide to modification, and no real support. What to do? The products were due to be shown in early January, 1979, at the Consumer Electronics Show (CES) in Las Vegas, Nevada. "