I have always been keen on taking advantage of free offers. Given the choice between a fast food meal with a freebie or one without, I'll plump for the mystery envelope every time. It's human nature, and marketers know it well.

Even in 1979, when I bought my first home computer, there were user groups who supplied type-in listings for a nominal charge. When I bought the first of a series of Atari ST computers in the '80s and '90s, I was a regular customer and contributor to a public domain (PD) software library. Fast forward to the end of the '90s and I was distributing the source code to a number of simple educational flash games to other teachers over the internet.

So that's my credentials. Like many others, however, I have received much more from open source software than I have ever put in. For the uninitiated, it is worth explaining a few definitions here:

Shareware Software: is free to try, but there is a moral obligation to register your software with its creator and receive upgrades and support in return for a fee. The evaluation period may last for a reasonable length of time after which some features of the software may become unusable.

The Public Domain: if the creator of a work relinquishes all his rights to his intellectual property, it enters the public domain and can be used by others to create derivative works or profit from it without payment of any fees or need for some form of license.

License: many creators who wish to share their intellectual property with others will give away limited rights that allow the user to do a range of things - but still maintain overall control of the way their work is used. Many open source software developers will use the GNU Public License (GPL) as a framework for stating how their work can be used.

Open source software does not have to be synonymous with poorly written undocumented utilities that nobody else wants. Here are a few of my favourites:

Open Office: a fully-fledged office suite, word-processor, spreadsheet, presentation software and graphics package. The fact that these programs will export both PDF format to be read by Adobe Acrobat reader and SWF flash files for use on the web makes them incredibly useful to me. They are the main application software that I use on my laptop.

The GIMP: an image processing package with enough features to rival Photoshop. For younger artists, my daughters love Tux Paint with its variety of stamps and special features.

Moodle: an open source content management system specifically designed for educators. There are plenty of other open source CMS packages available for blogging or running your own web portal.

David Hellam is an international educator, currently working on a project at http://www.educator.pro to build a homepage for the professional educator.