OpenOffice.org is one of the main pretenders to the Microsoft Office throne, one of the few that can measure up to one of the most formidable office suites in the world. There's a number of features that differentiate OpenOffice.org from some of the other non-Microsoft office suites.

The first is simply that this is an open source product based on Sun Microsystems' StarOffice product. Open source means that the product is free and is supported by a community of users and developers. The second distinguishing feature is that the product is multi-platform; it can run under Windows, Linux, Solaris or Mac.

Acquiring OpenOffice.org is relatively straightforward - download the files from the eponymous Web site (it's a 30MB download) or purchase a boxed version of Sun's StarOffice. Installation is straightforward, though if you intend to use it with a database or some Java extensions then it makes sense to install a current Java run-time environment first (also available free from Sun) as you will be prompted for one during the install. Once installed the product takes up around 140MB of disk space, pretty much the same as Microsoft Office.

Whereas Microsoft Office is essentially structured around a set of distinct applications - Word, Excel, PowerPoint and Access - OpenOffice.org takes a more document-centric approach. When you open the program, either via the single icon installed on the desktop or via the quick-start icon in the system tray, you are asked what type of file you want to edit or create. Text documents open the Writer word processor, spreadsheets open the Calc component, Impress is used for presentation graphics and Draw is used for... well, you can guess.

Each of these applications stands comparison to the competition. The user interface is well structured and familiar; anybody who has used Microsoft Office will be able to use OpenOffice.org without retraining. Obviously there are bound to be some differences but the overall look and feel is broadly similar.

Functionality is similar too, though some of the built-in templates are a little light compared to the Microsoft product (though it has to be added that this is better in the StarOffice version). On the other hand, the ability to save files as PDF is a function that is missing from some versions of the Microsoft suite, and HTML editing is also vastly superior in this product. Performance is good, even on older hardware.

One of the biggest barriers to adoption of competing products is file formats and here OpenOffice.org excels (pun intended). Support for Microsoft file formats is excellent. Complex Word, Excel and PowerPoint files were all opened, edited and saved without problem in our tests. Furthermore, it is relatively easy to make these formats the defaults, so that all files are saved as Word, Excel or PowerPoint files. In the case of spreadsheets even complex formulae and charts converted without problem.

It is impossible not to be impressed by OpenOffice.org, particularly in the light of the continued feature creep of competing products. Add to that the fact that this is free software and it's hard not to conclude that it's a real winner. 16 million downloads can't be wrong, can they?