By Ivan Noble BBC News Online

An alternative browser based on open source software which has been more than four years in the making is now available to download from the net.

Test versions have been available for years but this is the first time that the ambitious project team have felt happy enough with their creation to call it Mozilla 1.0.

Mozilla is quick, stable, and virtually free of the default links to manufacturers' products that feature so prominently in commercial browsers.

Its developers aim it at companies wanting a browser to put in their own products.

But there is nothing to stop ordinary users downloading it to replace Microsoft's Internet Explorer or Netscape's Navigator.

Open recipe

Mozilla is a high-profile example of open source software.

Mozilla has a familiar feel for Netscape users

Developers of open source software give the public access to the hundreds of thousands of lines of instructions used to build their product.

Anyone with the right skills can change or improve the way the software works.

This way of doing things undermines the traditional way companies make money from selling licences to use their software.

But it does not stop firms making money from installing, supporting and configuring the software, and, its supporters argue, leads to higher quality software.

Opponents like Microsoft's Bill Gates say open source software deprives companies of intellectual property and governments of tax revenue.

War veteran

Mozilla was born in 1998, when, as the Microsoft-Netscape browser war was at its height, Netscape decided to open up the computer code it used to build its browser, Netscape Navigator.

Mozilla 1.0 will be compared against the fifth or sixth generation of commercial browsers

Mitchell Baker, Mozilla.org

A team of programmers, some volunteers, many sponsored by Netscape and other companies, set out to overhaul the code and make the browser more compatible with emerging internet standards.

The deeper they looked into the code, the more apparent it became that they would have to throw much of it away and start from scratch.

"This was a tough decision and it meant re-writing a large portion of the code," explained Mitchell Baker of mozilla.org, the site home to the Mozilla project.

Grappling with Gecko

The team rewrote the guts of their browser, the part which turns web page code stored into HTML files into text, images and layout on screen.

This component, the rendering engine, has a crucial impact on the speed and stability of the browser software.

The Mozilla team are fond of lizard references and codenamed their engine Gecko.

Netscape were so pleased with it that they put it and a test version of Mozilla at the heart of their Netscape 6 series of browsers.

So Mozilla has a familiar feel for Netscape 6 users, and its developers are conscious of what it will have to compete with.

Industry adoption

"It won't be judged by standards generally applied to the first release of products," Ms Baker told BBC News Online.

"Mozilla 1.0 will be compared against the fifth or sixth generation of commercial browsers," she said.

AOL, part of Netscape's parent company, AOL Time Warner, is testing a browser based on Mozilla's Gecko and may use it to replace its current version of Microsoft Internet Explorer.

Compuserve, part of the same conglomerate, already uses Mozilla.

The Mozilla release comes not long after the release of OpenOffice 1.0, a suite of office software produced to rival Microsoft Office, backed by Sun Microsystems and similarly free to download.

Both products run not just on Windows, but on a range of other operating systems.