To help distinguish libre (freedom) software from gratis (zero price) software, Richard Stallman, founder of the free software movement, developed the following explanation: "Free software is a matter of liberty, not price. To understand the concept, you should think of 'free' as in 'free speech', not as in 'free beer'". More specifically, free software means that computer users have the freedom to cooperate with whom they choose, and to control the software they use. The GNU Manifesto contains language that gives evidence of Stallman's initial confusion with the usage.
According to Richard Stallman and the Free Software Foundation, software is free software if people who receive a copy of the software have the following four freedoms:
- Freedom 0: The freedom to run the program for any purpose.
- Freedom 1: The freedom to study and modify the program.
- Freedom 2: The freedom to copy the program so you can help your neighbor.
- Freedom 3: The freedom to improve the program, and release your improvements to the public, so that the whole community benefits.
Freedoms 1 and 3 require source code access, because studying and modifying software without its source code is highly impractical. Access to annotated source code relieves these problems.
Other groups have published their own definitions which describe an almost identical set of software. The Debian Free Software Guidelines is one, and the Open Source Definition is another.
The free BSD-based operating systems, such as FreeBSD, OpenBSD, and NetBSD, don't have their own formal definitions of free software. Users of these systems find the same set of software to be acceptable, however, rather than advocate the use of copyleft free software licences, they see copyleft as being merely tolerable. Instead, they advocate permissive free software licences which allow others to make software based on their source code and then not, in turn, also distribute the source. Their view is that this permissive approach is more free. The Kerberos, X.org, and Apache software licences are substantially similar in intent and implementation. All of these software packages originated in academic institutions interested in the widest possible technology transfer (
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