SEATTLE — Few golden geese in technology have survived as long as Office has for Microsoft.

The suite of applications that includes Word, Excel and PowerPoint, first released in 1990, generated nearly a third of Microsoft’s revenue during its last fiscal year — about $26 billion of $87 billion in total. By some estimates, the software accounted for an even higher portion of the company’s gross profits.

But in a sign of the seismic changes underway in the tech industry, Microsoft, the world’s largest software company, said on Thursday that it would give away a comprehensive mobile edition of Office. The free software for iPads, iPhones and Android tablets will do most of the most essential things people normally do with the computer versions of the product.

Just a few years ago, giving away a full free version of Office would have earned a Microsoft chief executive a visit from a witch doctor. Now, the move is following through on the rallying cry coming from Satya Nadella, Microsoft’s new chief executive, who has pushed cloud and mobile computing as lodestars for the company’s future.

The old Microsoft hemmed and hawed about creating Office apps for mobile platforms from Google and Apple, pushing its Windows platform instead. But the center of gravity in the tech industry has quickly shifted to mobile and cloud computing. And the company’s about-face comes after rivals like Apple and Google and many of the most successful new start-ups offered free software, often with premium perks for sale.