ISTORY is rife with unlikely pairs: van Gogh and Gauguin. Felix and Oscar. Lyle and Julia. But Tux, the jolly black-and-yellow Linux penguin, and Bill Gates?

Indeed, the unthinkable has happened: an informal partnership between a Microsoft project called .Net and an ordinarily Microsoft-bashing camp of programmers who have set out to produce a free twin of the .Net framework, a set of programming tools. The effort, called Mono, is a rare bridging of the chasm between the commercial world and free software, a movement in which the Linux operating system is at the forefront.

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At first glance, the cooperation might seem counterproductive for Microsoft, since the effort will produce a free alternative to Microsoft's own programming tools. But while the project aims to help programmers who write code in Linux, those programmers would be creating software compatible with the Windows operating system and with .Net (pronounced dot-net) — a result Microsoft welcomes as a way to help make .Net a lingua franca.

The two-year-old .Net initiative, promoted by Microsoft as the next generation in computing architecture, is a complex beast. Put simply, it is a framework for running programs, like word processors and spreadsheets, over a network. In the same way the Internet connects people over long distances or across the room, .Net will in theory connect programs, devices and data using a defined set of protocols and programming tools, a process that has typically taken hours of programming just to produce one or two simple connections.

Although many programmers discount the Microsoft system as derivative and even unimportant, the founder of the Mono project, Miguel de Icaza, sees it as a vision of the future. The best part, said Mr. de Icaza, the 29-year-old chief technical officer at Ximian in Boston, is that it reduces the cost of building a big program. Instead of rewriting old programs or translating them so that they will work on diverse operating systems, programmers can simply write a compact piece of code and, using the .Net framework, be relatively sure that it will work well on many systems, including hand-helds, tablet computers and any number of future devices.

The .Net initiative was born in part from the competition between Microsoft and Sun Microsystems, with its Java programming language. "Microsoft saw that a lot of companies were going to move to Java if they didn't improve their programming systems," Mr. de Icaza said. "They needed to get a better set of development tools."

Sun Microsystems designed Java to offer the sort of versatile tools that the .Net system is now setting out to provide. The Java system has a number of open-source versions available, including one designed by the Blackdown project (blackdown.org).

By the same token, Mono — taken from the Spanish word for monkey — is an attempt to create a free version of .Net. But Microsoft was keen to point out that the Mono project is only a subset of the complete .Net framework. For some more powerful functions, users will still have to turn to Microsoft's own programming tools, which can cost $700 for individual developers and more than $2,300 for business customers.

Microsoft has traditionally kept tight control over its programming languages and systems. But David Stutz, a lead engineer in Microsoft's .Net efforts, said the company was glad to see Mr. de Icaza's project grow as a way to help fill the marketplace with .Net-based programs.

"This is a very important technology for Microsoft," he said. "It's important to get this adopted." Microsoft may be facing a monumental antitrust case, but where .Net is concerned, Mr. Stutz said, "we can't push the market share and force people to use our system."

More than 50 volunteer programmers from around the world are translating a set of Microsoft specifications into a workable clone of the .Net project. The year-old Mono project is at a stage where even casual programmers could write .Net-compatible applications.

Ximian intends to integrate Mono into a larger open-source project, Gnome, an interface that makes Linux easier to use. Some of the resulting software may run on both Linux and Windows operating systems — a tantalizing prospect for governments and educational organizations that have expressed growing interest in Linux, in large part as an alternative to dependence on Microsoft's software.

When Mr. de Icaza first announced the Mono project, some in the Linux camp expressed outrage, calling it blasphemous, even dangerous. "Some people seem to think that Microsoft might use its legal clout to shut down Mono" if it no longer suited Microsoft's purposes, said Don Marti, 34, editor in chief of Linux Journal.

Mono supporters, however, have concluded that change is good.

"I think that a good idea is a good idea, regardless of where it comes from," said Talbott Crowell, 35, a consultant at Third Millennium in Lexington, Mass., and a Mono programmer. "To favor older systems over new alternatives out of loyalty is destructive to ingenuity and stifles creativity."

Mr. de Icaza and the Mono team based its system on public specifications that Microsoft submitted to an international standards body, a typical move for any software company wanting to make its technology a standard. He acknowledged that many Linux partisans fear that quarter given to Microsoft is ground taken away from free software projects like Linux but say that Mono can only improve the "software ecosystem."

He said Microsoft employees had been readily available to explain the finer points of the technology or give advice, something that would have been unheard of in previous years.

"I see them at conferences and can ask them a few questions now and then," he said. "There's no official support, but they're helpful."