Four Freedoms (software) foundational text GNU Manifesto
Freedom 0: The freedom to use the program for any purpose.
Freedom 1: The freedom to study how the program works, and change it to make it do what you wish.
Freedom 2: The freedom to redistribute and make copies so you can help your neighbor.
Freedom 3: The freedom to improve the program, and release your improvements (and modified versions in general) to the public, so that the whole community benefits.Freedoms 1 and 3 require source code to be available because studying and modifying software without its source code can range from highly impractical to nearly impossible.
Thus, free software means that computer users have the freedom to cooperate with whom they choose, and to control the software they use. To summarize this into a remark distinguishing libre (freedom) software from gratis (zero price) software, the Free Software Foundation says: "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'". (See Gratis versus libre.)
In the late 1990s, other groups published their own definitions that describe an almost identical set of software. The most notable are Debian Free Software Guidelines published in 1997, and The Open Source Definition, published in 1998.
The BSD-based operating systems, such as FreeBSD, OpenBSD, and NetBSD, do not have their own formal definitions of free software. Users of these systems generally find the same set of software to be acceptable, but sometimes see copyleft as restrictive. They generally advocate permissive free software licenses, which allow others to use the software as they wish, without being legally forced to provide the source code. Their view is that this permissive approach is more free. The Kerberos, X11, and Apache software licenses are substantially similar in intent and implementation.
core text primary text essential document basic text fundamental document