For most computer users, Microsoft Office is like the microwave oven. No one quite remembers when it became ubiquitous and few can imagine life without it. The software suite has a 90 per cent plus share of the business software market and is a cornerstone of the Microsoft empire, accounting for a third of the company's total revenues.

But a challenger has entered the ring, hoping to break Office's hold on the market. For businesses worried about the cost of Microsoft's new software licensing scheme, the timing couldn't be better.

OpenOffice is an integrated business suite with a word-processor, spreadsheet, presentation and drawing program. It is available in 25 languages, is Office-compatible and also cross-platform, working on Windows, Linux and, soon, Mac. But the best news is that it is completely free.

OpenOffice began life in the 1980s as a German office suite, StarOffice, and was taken over by Sun Microsystems in 1999. A year later Sun decided to follow the example of the Linux operating system and released the StarOffice source code to programmers.

Two years later, the first full version of the open-source program has been released and the result should make Microsoft nervous.

The aim of OpenOffice programmers seems to have been to overcome the biggest inhibition users have to switching programs: the familiarity of the old and teething problems with the new. To do this they have followed the age-old philosophy, if you're going to steal, steal from the best.

OpenOffice menus, shortcut keys and many icons have been directly lifted from Office. Writer, the word processor, is a clone of Word while Excel users will feel at home in the Calc spreadsheet.

The fun lies in discovering the less-obvious features that improve on Office. For instance, the AutoComplete function recognises hundreds of words as you type compared to a few dozen words recognised in Word. OpenOffice has no problems with frames, columns, tables and mail merges. Neither has it any difficulty reading Office files; the program can save files automatically in the Office format or its own more compact format. A 500-page document that takes up 1.2MB of disk space as a Word document is a quarter of the size, just over 300K, when saved as a Writer file. But the zero price tag does mean some sacrifices. OpenOffice lacks proper database and e-mail programs and some of Office's less well-known features such as collaboration tools and Web-based elements.

But as technology website ZDNet wrote: "Considering that 80 per cent of the people who use office suites use them for 20 per cent of their features, StarOffice is the functional equivalent of Microsoft Office."

OpenOffice is simple to use and stable, given its open source origins. Like the Linux operating system, the program is developed and maintained by a worldwide network of volunteer programmers. Users who are not programmers are welcome in the OpenOffice internet forum where they can get help and submit requests for improvements to be included in the next release.

Sun has released a commercial version of OpenOffice called StarOffice 6.0 (£45.99 sterling from amazon.co.uk) that offers some extra features, a printed manual and a technical support option.

The program has been positively received in the US, but the biggest boost to OpenOffice's chances has come from Microsoft itself. The firm's plan to force businesses to buy three-year subscriptions for software updates threatens to alienate small and medium business users, particularly those who do not buy every Office upgrade. Their frustration might encourage them to migrate to OpenOffice and could drive up the free software's market share to 10 per cent by 2004, according to report by consultants Gartner.

Another independent study by US-based Giga Information concluded it was likely that Microsoft Office would remain in use in large firms in the future while smaller and medium firms sought alternatives such as OpenOffice.

"Microsoft may be compelled to release a 'light' version of Microsoft Office to remain competitive," said Giga in its report. "As competing low-cost alternatives grow more robust, Microsoft will be forced to innovate or lose market share."

Budget airlines have shown how succesful a no-frills, low-cost alternative can be. OpenOffice has all the essential frills of Microsoft Office for the lowest possible price. Minutes after installing OpenOffice, this user was quite happy to delete Microsoft Office from his hard drive.

One user less, Bill.

OpenOffice 1.0 is available to download from www.openoffice.org