This is a story about innovation, legacy, and a surprising thing most people don't remember about Apple's early days. And it comes just as Apple is embarking on yet another new strategy.

The story starts for our purposes from an impassioned interview that Steve Jobs gave two decades before his death, in which he talked talked about the single, long-forgotten software program without which he said Apple likely wouldn't have succeeded.

That program -- the very first computer spreadsheet -- called VisiCalc, made its debut at a computer expo in Manhattan exactly 40 years ago this week.

Almost nobody noticed at the time, but VisiCalc became the "killer app" that prompted widespread adoption of the Apple II computer in the early 1980s.

"VisiCalc," Jobs said in the 1990 television interview. "And that's what really drove, propelled the Apple to the success it achieved, more than any other single event."

'All hail VisiCalc'

Contemporary news stories talk about businesspeople going to computer stores to buy the groundbreaking $100 VisiCalc program, and then buying their first computers -- the $2,500 Apple II -- when they realized it was the only computer VisiCalc could run on.

(Inc. wrote about it back then, saying, "The significance of VisiCalc isn't that it's full of whiz-bang technical features, but that it's written for non-technical people.")

But it wasn't an Apple product. Its creators were Dan Bricklin, a computer programmer who attended Harvard Business School in the late 1970s, and a former colleague named Bob Frankston.

Bricklin came up with the idea for the spreadsheet during an HBS class, and he then designed a prototype version. Then, Frankston worked via dialup from the attic of a rented apartment to program it.

Among the key problems they solved that we now take for granted: lettering the columns and numbering the rows, so that they knew how to refer to each individual cell.

They wound up distributing through a software publishing company launched by another Harvard graduate, Daniel Fylstra. Brlcklin explained in his talk what happened next:

In June of 1979, our publisher announced VisiCalc to the world, in a small booth at the giant National Computer Conference in New York City.

The New York Times had a humorous article about the conference. "The machines perform what seem religious rites ... 'All hail VISICALC.'" 

That was the last mention of the electronic spreadsheet in the popular business press for about two years. Most people didn't get it yet. But some did. 

The rise and the fall

More than a million copies of VisiCalc were sold between 1979 and 1983. 

As The Wall Street Journal put it in a retrospective around the same time Jobs gave his interview, because of VisiCalc, "suddenly legions of business-school graduates, accountants and others who pushed numbers around for a living for the first time had a reason to own a PC."

But its dominance was short-lived.

A product manager who had worked for Fylstra's company, Mitchell Kapor, negotiated an exit from the company, signing over everything he'd created, as the New York Times described contemporaneously, "with one exception -- a product he described in a one-page document attached to the buyout agreement."

Kapor started his own company and turned that single product into a better spreadsheet program called Lotus 1-2-3, which ran better than VisiCalc did on IBM's new computers.

'You'd be interviewing somebody else'

Once, companies had bought Apple II computers to run VisiCalc; now they were "buying $5,000 IBM personal computer systems simply to run a $495 spreadsheet," Kapor told Vox in 2014.

Eventually, the company Bricklin and Frankston started wound up in a giant lawsuit with Fylstra's company, which he'd now renamed Visicorp.

Meanwhile, Kapor's Lotus 1-2-3 did $53 million in its first year. Eventually, IBM bought it outright. Of course, as a spreadsheet it was ultimately overcome by Microsoft Excel, Google Sheets, and many others.

Still, before all those there was Lotus 1-2-3, and before Lotus 1-2-3, there was VisiCalc. And Jobs was very clear in how crucial it was to the early success of Apple.

"If Visicalc had been written for some other computer," he told his interviewer in 1990, "you'd be interviewing somebody else right now."