Movement has spread beyond Linux to embrace a range of the core software programs that run corporate computer systems and networks

These days, it seems, no self-respecting software visionary wants to become Mr Bill Gates.

Forget the money, the fame and the power: the Microsoft chairman is an anachronism. The model of software he represents - a technologically closed world where one company develops and controls access to the product - is history.

That, at least, is the version of events being peddled by a growing band of technology industry subversives. Many of these promoters of so-called "open source" software have drawn their self-confidence from the success of Linux, one of the most startling technological ideas of recent years. The movement has already spread far beyond Linux to embrace a wide range of the core software programs that run corporate computer systems and networks.

All of this represents an experimental model for software development that has gained ground surprisingly quickly in the normally conservative corporate information technology world.

It has been enough to prompt a warning from the company that has benefited most from the traditional commercial model for software development. In a memo to Microsoft staff earlier this month, Mr Steve Ballmer, chief executive, warned: "Non-commercial software products in general, and Linux in particular, present a competitive challenge for us and for our entire industry, and they require our concentrated focus and attention."

As with the sudden emergence of the internet in the mid-1990s, Microsoft's willingness to take this unexpected new threat so seriously could provide the strongest indication of its readiness to respond. "We will rise to the challenge," promised Mr Ballmer.

Open-source software comes in many flavours but they all share certain characteristics. The source code - the underlying instructions that determine how a program operates - is public, so users can tamper with it. Most open-source projects accept new code contributed by volunteers.

Most also use some form of the General Public Licence written for GNU, the software that provides much of the guts of the Linux operating system. This licence forces anyone who makes changes to the software to make their own adaptations freely available to others. However, many newer pro- jects use a limited version of the licence that is less stringent.

The variation in licences points to a growing experimentation with new business ideas aimed at building commercial operations on the traditional "community" foundations of open source. Critics claim this will kill the idealistic spirit behind the movement, though others contend it is a necessary development. "Those who try to be only free run out of energy and funding," retorts Mr Marten Mickos, the Swedish chief executive of MySQL, a company that controls an open-source database of the same name.

By selling commercial licences, MySQL represents part of a second wave of open-source companies with a new business model, says Mr Kevin Harvey. His firm, Benchmark Capital, was also an early supporter of Red Hat, now the leading Linux distributor.

So far, most open-source projects are concentrated in areas of "infrastructure" software - the code that runs the core activities of a computer or a network. This extends from the basic operating system to the "middleware" layers of software needed to run particular applications.

Cheap basic software of this type, which can be easily "commoditised", has been "key to the ubiquity of computing and the birth of the internet", says Mr Marc Fleury, the French founder of JBoss, which produces software for the application servers that handle many web transactions.

The reliability of core software like this is also vital to the security of computer networks - one reason that governments, in particular, like to examine the source code of the products they use. "The only way to be really sure is to go into the source code and make sure there are no backdoors or loopholes," says Mr Mickos. This is a message that has not been lost on Microsoft, which recently decided to give more governments a peek at its still private code.

Another reason for the success of some open-source projects is the explicit backing they get from powerful corporate interests. IBM's support of Linux helped give the operating system credibility in the corporate world. That put Microsoft on the defensive, as well as producers of Unix operating systems like Sun.

Other big companies have also tried to use open-source as a competitive weapon, though generally with less success. Netscape, beaten in the browser wars by Microsoft, released its source code publicly through the Mozilla project, Sun tried a similar route with OpenOffice, the source code for its version of Microsoft's highly successful Office suite. And SAP has thrown its weight behind the MySQL database - an apparent response to rivals such as Oracle and Microsoft, which have their own database products and now have their eyes on SAP's applications software market.

Linux's success is also helping propel the adoption of other programs, says Mr Eric Raymond, whose book The Cathedral And The Bazaar remains the most thorough examination of open-source development: "These projects are successful because they can be deployed on the Linux platform."

Microsoft's response to the open-source threat is to redouble its efforts to persuade customers its own software is worth paying for and to fine tune its marketing and development to make sure it keeps customers happy. It has also started to issue warnings that the open-source approach discourages innovation. Such accusations are quickly dismissed in open-source circles. Sure, the interfaces that determine the look and feel of some open-source products bear similarity to commercial versions, concedes Mr Raymond. But he says this likeness is superficial. "That's not what we're good at," he adds of the engineers whose efforts drive so many open-source projects. "We're good at the under-the-hood bits."

Most advocates of the genre claim a more simple and flexible architecture for their core software, reflecting the fact that, unlike commercial software makers, they are not under pressure continually to add new features to their products to generate sales.

The fact that so many start-up projects are enjoying a ride on the coat-tails of Linux suggests that big corporate users of software are at least willing to try out these new programs - even if it does not mean that Mr Gates is in trouble quite yet. - (Financial Times Service)