It is now available for businesses. Microsoft has said that Office will range in price from a limited, free Web version supported by ads to a full-blown version that costs $500, both to be available to consumers in June. Most analysts say they think Microsoft will hold on to its near monopoly on productivity software. Richard Williams, the senior software analyst at Cross Research, said that most companies would continue to choose Office because it was familiar and safe. “This is not the cycle that will take away from Windows or Office,” he said. “Most of the people calling the shots and paying the bills are in their 40s, and grew up with Microsoft.”

Nonetheless, a host of businesses are chipping away at Microsoft either by offering free versions or by recommending to clients that they buy fewer copies of Office. “I think Office has run away from its users,” said David Girouard, the president of Google’s business software group. “Every company ought to have a few copies of it, but it has nothing to do with what most people need.”

Users of the new version of Office will be able to share and work on the same documents and presentations over the Internet rather than e-mailing files back and forth to each other. Microsoft has created a way for people to flip from the PC to online versions of Office to give users the best of both worlds.

If many of those functions sound familiar, it is because Google, Adobe and smaller companies like Zoho have been giving away Web-based apps that do much the same thing. But the rival products have hardly made a dent in the sales of Office — a product used by 500 million people.

Over the last three years, Microsoft’s share of the office software market has remained static at 94 percent, according to the research firm Gartner. Adobe ranks second in office software revenue with almost 4 percent of the market, leaving scraps for about eight other companies. Microsoft’s business software group brought in $19 billion last year.