I considered including Linux, but that one's a bit obvious, isn't it?

Open source software has a lot going for it. The transparency of the whole process means that different sections of the same program are much more likely to work with each other, and also means that it's much easier to extend the functionality. Security holes are also therefore patched much more quickly, as they can be fixed by anyone, not just a centralised system. It's also generally free, which always helps.

And, of course, sometimes the software is very good on its own, regardless of any other factors. With that in mind, here's a short list of open source software that I'm particularly keen on. Click the pictures to go to the official websites.

Mozilla Firefox

Let's start with probably the best-known piece of open source software. Firefox is my personal browser of choice, and its market share is steadily growing. It's fast, very easily extensible (almost infinitely, in fact, if you take things like Greasemonkey into account), and statistically much more secure than Internet Explorer. There's the odd issue with website compatibility, but really, if you're designing websites in the full knowledge that they won't work in a major browser, the problem is with you rather than the end user. Oh, and there's a portable version which runs off a flash drive. Ideal, really.

Inkscape

You may be less likely to have heard of Inkscape, but when it comes to open source graphics programs, it's something of a gem - certainly better than the more famous GIMP, which I've never really got along with. Essentially, Inkscape does the same kind of thing as Adobe Illustrator - it produces very smooth vector graphics files which can be resized infinitely with no pixelation. Its ability to convert raster graphics (JPGs, GIFs and so on) to vector ones is also excellent - unless you really need an industry standard package, this will see you through.

OpenOffice.org

Despite apparently including a domain suffix in the official name of their product (I don't care how "21st Century" you think you are, it just looks silly), OpenOffice.org is a very impressive office suite. It's not really featherweight, coming in at over 90MB for the whole suite, but that's not bad compared to Microsoft's lumbering behemoth. And if you set it up right, it is almost indistinguishable in performance from any other office program available. There's one or two things which aren't quite the same (apparently going backwards through a presentation behaves slightly differently to Powerpoint), but that's more than made up for by the lack of the Office Assistant.

Audacity

Now we're getting into the really good stuff. Audacity isn't just one of the best open source projects I've come across, it's also hands-down the best audio editor I've ever used. It's easy to use, packed full of tools (the speed and tempo controls can be hilarious when used right) and tiny to boot (this is another one that easily runs off a flash drive). More importantly, its usability is superb. Need to move a snatch of audio back a bit in the file? Just highlight it and drag it along the timeline. That may sound obvious, but I'm yet to come across another program that will do it so simply.

The LAME MP3 encoder

Now here's one you might not have heard of, but if you've ever worked with MP3 files you've almost certainly used it. LAME is one of the most reputable methods for creating MP3s around - it certainly works well, and is used in all sorts of places. The official site claims that it's probably the only MP3 codec still under active development - not a bad idea, as MP3s have recently seen a resurgence with format wars on the horizon. (As far as the end user is concerned, that means it's one of the only formats that plays on your iPod. Motivation for further development, right there.)

Celestia

I just downloaded this one last night, and I've already spent ages simply playing with it, fascinated. It's an astronomy program, but not like any of the usual planetarium software. Rather, it gives you a 3D, almost fully explorable model of the entire Universe. Quite an ambitious goal, you might think, and you'd be right, but it's been realised very impressively. Any software which lets you zoom from the surface of the Earth past the limits of the observable Universe in about 10 seconds counts as a good piece of software as far as I'm concerned. Just don't play with it for too long, or you'll start to get spooked when you go off to investigate an interesting-looking galaxy and can't find the Sun any more...

7-Zip

Remember back when Windows didn't have native support for ZIP archives, and you had to use WinZip? And how it would nag you to buy a licence every single time you started it up? And how, even after you'd ignored it, it ran like a rhino through treacle? 7-Zip is like that, just without the nagging. Oh, and it's blazingly fast. So not very much like WinZip, in fact. If you need more control over archives than Windows offers, or you need to open different types of archive, this is the place to go.

Python

Another one that you may not have heard of, but you've definitely used it. Python is a programming language, and rather a powerful one at that - the reasons why get a bit technical, but suffice to say that it makes programming impressively straightforward. And, being even more easily extensible than Firefox, almost anything can be done with it - have a look at Blender, a program that nearly found its way into this list, to see what's possible. And what did I mean by saying that you've definitely used Python? Well, Google runs on it.

Even after that lot, we've barely scratched the surface of what the open source community has come up with. Look at this list to get an idea of what else is on offer. Essentially, no matter what you do with computers, there's something free and open which will do much the same thing. Looks worth investigating, wouldn't you say?