To outsiders, software whose source code is freely distributable is open source software. However, as soon as you become involved with the community that centers around such code, you quickly find that it is also called free software -- and that the two terms are far from synonymous. Which term you choose to use can quickly associate you with a whole spectrum of political and philosophical beliefs, and can make the difference between receiving cooperation and being ostracized. As a newcomer, you might easily imagine that you have stumbled out of the woods and into the target end of a rifle range, all because of your innocent choice of jargon.
To make matters worse, knowing which of the two phrases to use is difficult, because they are used in several different ways. At the most basic level, they indicate a specific organization and its principles. At another level, the choice of terms may reflect your audience. And, at the most important level, your choice may reflect your ethical imperatives and your vision of the future of computing.
All these meanings blur together, and are heavily dependent on context, so much so that members of the communities can switch meaning in mid-conversation, and sometimes even in mid-sentence. They also carry the baggage of over a decade of co-existence and personal animosities.
These subtleties cannot be learned overnight. After all, supporters of both free and open source use the same software and same licenses, and mostly seem to co-exist on a daily basis. However, if you are a newcomer to the world of free and open source software, what follows may provide a starting point to overcoming your confusion.
The idea that software source code should be freely distributable dates back to at least the early 1960s. However, it was the Free Software Foundation (FSF) that popularized the idea in modern times, referring to it as free software. The trouble with this term is that "free" is ambiguous in the phrase: It is meant to refer to personal liberty, but can easily be taken to refer to price. The FSF has long tried to clarify the phrase by adding "free as in freedom, not as in beer," but this explanation is not much help, since, as more than one humorist has pointed out, beer is rarely free.
Coupled with the activist, counter-cultural image of the community in the mid-1990s, the term "free software" seemed to some to be unfriendly to business -- and, therefore, to the acceptance of the software by a wider audience. For these reasons, a group of community members that included Larry Augustin, Jon Hall, Michael Tiemann, and Eric S. Raymond met in January 1998 brainstormed to find an alternate term.
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Their choice was "open source," a term used in the espionage community to refer to information available in public sources. Raymond and Bruce Perens founded the Open Source Initiative soon after, and, at a second meeting in April 1998 sponsored by publisher Tim O'Reilly, a group of project leaders voted to promote the use of the term.
In the ten years since, "open source" has become the most commonly used term outside the community -- so much so that Richard Stallman, founder and president of the FSF, frequently explains that he does not consider himself an open source advocate.
What is not often mentioned in official histories, such as the one on Wikipedia, is that part of the decision to use another term were personal feuds between several of those who attended the meetings and FSF supporters.
For instance, Perens and Stallman are known to have had at least one shouting match, although Perens has mellowed enough so that in his recent article to mark the tenth anniversary of the coining of open source, he refers to Stallman as a "giant" and speaks generously about him.
However, some of these early animosities survive to this day. In particular, Linus Torvalds retains a deep distrust of the FSF, so much so that, eighteen months ago, he refused to participate in the discussion about how to revise the Gnu General Public License (GPL). "The FSF considers us open source people 'heretics,' he wrote to me at the time, dismissing the consultation process as a public relations exercise, and even the efforts to make the GPL compatible with the Apache License as an effort to "hijack" projects.
For its part, the FSF is equally dismissive about Torvalds. Peter Brown, the executive director of the FSF, although not involved in the clashes of a decade ago, nonetheless echoes them when he told me, "There's this basic clash of people who are afraid of the Free Software Foundation and Richard Stallman, and portray him as somehow destroying and as ruining everything for everyone. Don't portray [Torvalds] as the leader of a movement that wants people to have control of their computers. He doesn't believe in that stuff. People have crowned him the leader of a movement when he's not. He's the leader of a software project."
These old feuds are worth remembering as you struggle to understand why the distinction between "free" and "open source" is so full of consequences. If nothing else, they help to explain why people feel so strongly about such an apparently innocuous subject.