Free software

:This article is about Free Software as defined by the sociopolitical Free Software movement; for information on software distributed without charge, see freeware. For other uses, see free software (disambiguation).

Free software licenses

According to Stallman and the FSF, "free" software licenses grant:

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• the freedom to run the program for any purpose (called "freedom 0")
• the freedom to study and modify the program ("freedom 1")
• the freedom to copy the program so you can help your neighbor ("freedom 2")
• the freedom to improve the program, and release your improvements to the public, so that the whole community benefits ("freedom 3")

Freedoms 1 and 3 require source code access, because studying and modifying software without source code is extremely difficult and highly inefficient compared to modifying annotated source code.

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The FSF web site provides a list of many free software licenses. http://www.gnu.org/licenses/license-list.html The list is necessarily incomplete, because a license need not be known to the FSF in order to provide these freedoms.

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"Proprietary software" is distributed under more restrictive software licenses. Copyright law and/or contract law restrict modification, duplication and redistribution by users; software released under a free software license rescinds most of these reserved rights.

Related Topics:
Proprietary software - Software license - Copyright - Contract

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The FSF free software definition disregards price. CDs containing free software such as GNU/Linux distributions are commonly for sale. However, since the CD buyer still has the free software freedoms, it is free software. Free beer software (freeware) which includes restrictions that confict with the FSF definition are considered proprietary. For example, source code may be unavailable, redistributors may be prohibited charging fees, etc.

Related Topics:
CDs - GNU/Linux distributions - Freeware

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Some people use "libre" to avoid the ambiguity of the word "free". However, these terms are mostly used within the free software movement and are slowly spreading.

Related Topics:
Libre - Free software movement

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Variations on free software as defined by the FSF:

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• Copyleft licenses, the GNU General Public License being the most prominent. The author retains copyright and permits redistribution and modification under terms to ensure that all modified versions remain free.
• Public domain software - the author has abandoned the copyright. Since public-domain software lacks copyright protection, it may be freely incorporated into any work, whether proprietary or free.
• BSD-style licenses, so called because they are applied to much of the software distributed with the BSD operating systems. The author retains copyright protection solely to disclaim warranty and require proper attribution of modified works, but permits redistribution and modification in any work, even proprietary ones.

A copyright owner of copyleft-licensed software can produce and sell a version under any license, in addition to distributing the original version as free software. Many free software companies do this; this does not restrict any rights granted to the users of the copyleft version.

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All free software licenses must grant people all the freedoms discussed above. However, unless the applications' licenses are compatible, combining programs by mixing source code or directly linking binaries is problematic, because of license technicalities. Programs indirectly connected together may avoid this problem.

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