His death was confirmed by his son Allan.
For a time, Kay's company, Kaypro, was the world's largest portable computer maker, ranked fourth in the PC industry overall behind IBM, Apple Computer and RadioShack.
Early on, the Kaypro II developed a loyal following. Arthur C. Clarke used a Kaypro to write his novel "2010: Odyssey Two"; Stephen M. Case, who would become chief executive of America Online, bought one as his first computer, adding a 300-baud modem to explore the fledgling online world.
"The Kaypro computer was a necessary step in getting to the iPad," Paul Freiberger, co-author of "Fire in the Valley: The Making of the Personal Computer," said in an interview Friday. "Back then few thought of making a computer you could carry around. It was loved because he got almost everything right."
The Kaypro II burst onto the scene in 1982 at the West Coast Computer Faire in San Francisco. The hobbyist phase of the industry was just ending, and although IBM had entered the personal computer market the previous year, portable computers were still a novelty.
The 1981 exposition was dominated by Adam Osborne's trailblazing Osborne I computer, which weighed 24 pounds, had a 5-inch display and came with a handful of programs for what was then a breakthrough price: $1,795.
The next year Kay's boxy computer appeared at the same event, downstairs in a tiny booth in what was normally an underground parking garage. The Kaypro II generated a great deal of enthusiasm by surpassing many of the Osborne's features.
Both machines were described as "luggables" and were the size of portable sewing machines. But the Kaypro's case was rugged metal, in contrast to the Osborne's plastic shell, and it had a 9-inch cathode ray tube display. It weighed 29 pounds and, like the Osborne I, sold for $1,795.
Later that year, Kay's fledgling company benefited when Osborne announced plans for a new model, effectively killing sales of the firm's existing machine. This failure of business strategy became famously known as the "Osborne effect." By the end of 1983, Osborne's company was bankrupt.
Neither the Osborne I nor the Kaypro II initially ran the MS-DOS operating system, which would ultimately be an Achilles' heel as the software world catalyzed around the IBM PC and the software platform Microsoft had developed for it.
Kay came to the personal computer industry when he observed that his son-in-law was having trouble moving a bulky Apple II that came with a separate monitor. It occurred to him that an all-in-one machine would be more portable. At the time, Kay owned a small company that made electronics test equipment for the aerospace industry in Southern California.
The idea for a portable computer arrived just in the nick of time. His firm, Non-Linear Systems, had originally grown on the strength of the military and space industries. But after the Apollo space program ended in the early '70s, the company foundered and lost money for a number of years.
Kaypro's revenue exceeded $120 million in 1985. But the company never successfully made the transition to the IBM-compatible world. It filed for Chapter 11 bankruptcy protection in 1990, and Kay, putting up $250,000 of his family's money, asserted, "We'll build up our independent dealer base and do it again.''
Kaypro was not able to emerge from bankruptcy, however, and its assets were liquidated in 1992.
Andrew Francis Kopischiansky was born Jan. 22, 1919, in Akron, Ohio, and received an engineering degree from the Massachusetts Institute of Technology in 1940.
After moving to California in 1949, he went to work at the Jet Propulsion Laboratory, where he was involved in the Redstone rocket development program. His family changed its surname to Kay that same year.
He founded Non-Linear Systems in 1952 and invented the digital voltmeter in 1954 after he decided that analog voltmeters, which displayed current values with a movable needle, were not accurate enough. Kay's voltmeter used a system of lights to display numeric values.
In addition to his son Allan, his survivors include another son, David; two daughters, Janice Kay Batter and Nancy Egli; and 14 grandchildren.
Allan Kay said his father was first and foremost an inventor. The Kay children, he recalled, were able to watch "Hopalong Cassidy" on a homemade television projection system, with the picture displayed on a plywood board that was painted white and hung on the wall of the family home.Catch the latest from the Consumer Electronics Show on Gadgets 360, at our CES 2026 hub.