I.B.M. has since tried to challenge Microsoft with a program called OS/2.

Still, industry executives remain skeptical about I.B.M.'s ability to challenge Microsoft, even with Lotus.

In its announcement, Oracle challenged Microsoft directly, saying it planned to use the new programs to outpace Microsoft as the company developers would turn to.

European competitiveness officials have not been shy about challenging Microsoft.

In doing so, Google will more openly challenge Microsoft and its office productivity tools, like Excel and Word, which users must buy for hundreds of dollars.

Netscape, for example, was supposed to be a technology giant to challenge Microsoft - now it's basically a provider of chat-room software.

It has gone through a radical transition in products, financing, and staff, now a very different company from the one which challenged Microsoft and Lotus in the early 1990s.

Oracle plans to announce a software system for interactive television, which analysts say could challenge Microsoft.

Novell has been widely reported to be looking for ways to challenge Microsoft beyond the F.T.C.'s investigation.

Jobs insists that an improved operating system could well enable Apple to challenge Microsoft, much as the Macintosh challenged I.B.M. technology 10 years ago.