The great Open Source giveaway

If you've been to a computer show in recent months you might have seen it: a shiny silver drink can with a ring-pull logo and the words "opencola" on the side. Inside is a fizzy drink that tastes very much like Coca-Cola. Or is it Pepsi?

There's something else written on the can, though, which sets the drink apart. It says "check out the source at opencola.com". Go to that Web address and you'll see something that's not available on Coca-Cola's website, or Pepsi's - the recipe for cola. For the first time ever, you can make the real thing in your own home.

OpenCola is the world's first "open source" consumer product. By calling it open source, its manufacturer is saying that instructions for making it are freely available. Anybody can make the drink, and anyone can modify and improve on the recipe as long as they, too, release their recipe into the public domain. As a way of doing business it's rather unusual - the Coca-Cola Company doesn't make a habit of giving away precious commercial secrets. But that's the point.

OpenCola is the most prominent sign yet that a long-running battle between rival philosophies in software development has spilt over into the rest of the world. What started as a technical debate over the best way to debug computer programs is developing into a political battle over the ownership of knowledge and how it is used, between those who put their faith in the free circulation of ideas and those who prefer to designate them "intellectual property".

No one knows what the outcome will be. In a world of growing opposition to corporate power, restrictive intellectual property rights and globalisation, open source is emerging as a possible alternative, a potentially potent means of fighting back.

The open source movement originated in 1984 when computer scientist Richard Stallman quit his job at MIT and set up the Free Software Foundation. His aim was to create high-quality software that was freely available to everybody. Stallman's beef was with commercial companies that smother their software with patents and copyrights and keep the source code - the original program, written in a computer language such as C++ - a closely guarded secret.

Stallman saw this as damaging. It generated poor-quality, bug-ridden software. And worse, it choked off the free flow of ideas. Stallman fretted that if computer scientists could no longer learn from one another's code, the art of programming would stagnate.

Stallman's move resonated round the computer science community and now there are thousands of similar projects. The star of the movement is Linux, an operating system created by Finnish student Linus Torvalds in the early 1990s and installed on around 18 million computers worldwide.

What sets open source software apart from commercial software is the fact that it's free, in both the political and the economic sense. If you want to use a commercial product such as Windows XP or Mac OS X you have to pay a fee and agree to abide by a licence that stops you from modifying or sharing the software.

But if you want to run Linux or another open source package, you can do so without paying a penny. You can also modify the software in any way you choose, copy it and share it without restrictions.

This freedom acts as an open invitation - some say challenge - to its users to make improvements. As a result, thousands of volunteers are constantly working on Linux, adding new features and winkling out bugs. Their contributions are reviewed by a panel and the best ones are added to Linux.

To maintain this benign state of affairs, open source software is covered by a special legal instrument called the General Public License. Instead of restricting how the software can be used, as a standard software license does, the GPL - often known as a "copyleft" - grants as much freedom as possible.