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The rapid spread of free software has produced prosperity in the real world

As you know, Saturday 15 September is (or was, depending on when you are reading this) Software Freedom Day. What, you mean you didn't know? Perhaps you think that the freedom of software doesn't mean much to you. Perhaps you don't think you use free software. Well, you do, if you use Google - in fact, if you use rather a good many other popular websites, too. The open-source software project Apache has been the most popular web-server software on the internet since 1996. Many, including the New Statesman, pair it with the Linux operating system to drive the machines that serve their websites.

You may even have downloaded some free software on to your computer if you use the increasingly popular web browser Mozilla Firefox. And if you're a clever Firefox user, you'll be using one of the many user-contributed "plug-ins" that alter your online browsing experience with their slick and kooky additional functionality.

But if this software is so commonplace, then why of all things should we celebrate its freedom? Isn't that as absurd as celebrating the freedom of your fridge to keep your milk fresh, or the freedom of your toaster to toast your toast?

Maybe, but let's go with it for a while. The Free Software Foundation, founded by the founder of free software itself, Richard Stallman, is one of the sponsors of Software Freedom Day. Its definition of such software is based around four freedoms. Freedom 0 (a good computer scientist always starts counting at zero) is the freedom to run a program for any purpose. Freedom 1 is the freedom to examine that program, to pick it apart and to put it back together again in a way that suits you and what you want to do with it - then share those changes both to "help your neighbour" (Freedom 2) and "so that the community benefits" (Freedom 3).

Despite the moral tone, it is not only faith that has contributed to the success of free software. The GPL, or General Public Licence - the legal embodiment of Freedoms 0-3, hacked out of copyright law - has guaranteed the spread of free and open-source software by, in effect, mandating sharing.

One result of this legal obligation to share has been the rapid innovation that has characterised the rich growth of the worldwide web. Through mass collaboration on complicated problems and through idiosyncratic innovation on the edges of the network - each of which relies on software being free - robust and reliable applications that power real-world prosperity and growth have been created.

So, software freedom might seem like an odd thing to celebrate at first, but consider. This odd little aspect of the information age is the first time, in a while at least, that we've seen what can happen when we all share nicely.