The term free software is used in essentially two different ways:
Software that can be used, copied, studied and modified and redistributed by the user;
Software which may be copied and used without payment, also referred to as freeware (or gratis software by advocates of the first variety).
These definitions may conflict, and a piece of software that is free in the first sense may not be free in the second, and vice versa.
Amongst software developers and free and open source software enthusiasts, the first sense is traditionally called "free as in free speech", while the second is called "free as in free beer". In this context, the term "free software" more commonly refers to the first sense. Advocates of "free as in speech" software call the second type "gratis", which translates to the "free" of "free beer," because there is no charge to receive a copy.
In many languages the terms for free as in freedom and free as in "free beer" is different; in French, for example, "libre" translates to "free" in the sense of "freedom". Hence, free software of the "free speech" type is sometimes called "software libre", from the French "logiciel libre" and the Spanish "software libre".
Free software of the first type is often made available online without charge, or available offline for the cost of distribution; however, this is not required, and free software can also be sold for profit.
Stallman introduced the concepts of "free software" and "copyleft", which he specifically devised to give users freedom and to restrain the possibilities for proprietisation .
The FSF has produced a specific free software definition, by which software is "free" in this sense if it grants:
the freedom to run the program for any purpose (freedom 0)
the freedom to study and modify the program (freedom 1, which they state requires access to the program's source code)
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)
A list of compliant licenses is available from FSF's web site (see below). The term "proprietary software" is used for software distributed under more restrictive licenses which do not grant these freedoms. Copyright law reserves most rights of modification, duplication and redistribution for the copyright owner; software released under a free software license specifically rescinds most of these reserved rights.
The FSF definition of free software does not touch on the issue of price; a commonly used slogan is "free as in speech, not as in beer", and it is common to see CDs of free software such as Linux distributions for sale. However, in this situation the buyer of the CD would have the right to copy and redistribute it.
Free beer software can include restrictions that do not conform to the FSF definition — for example, gratis software may not include source code, may actively prohibit redistributors from charging a fee, etc.
To avoid confusion, some people use the words "libre" and "gratis" to avoid the ambiguity of the English word "free". However, these alternative terms are still used mostly within the free software movement and are only slowly spreading to the outside world. Others advocate the term open source software, but the relationship between "open source" and "free software" is complex.
There are several variations on free software in the FSF sense, for example:
The freedoms defined by the FSF are protected through copyleft licenses, the most prominent of which is the GNU General Public License. The author retains copyright, and permits redistribution and modification under terms designed to ensure that all modified versions of the software remain under copyleft terms.
Public domain software, in which the author has abandoned the copyright. Public-domain software, since it is not protected by copyright at all, may be freely incorporated into closed, proprietary works as well as free ones.
BSD-style licensess, so called because they are applied to much of the software distributed with the BSD operating systems. The author under such licenses retains copyright protection solely to disclaim warranty and to require proper attribution of modified works, but permits redistribution and modification, even in proprietary works.
Note that the original copyright owner of copyleft-licensed software can also make a modified version under their original copyright, and sell it under any license they like, in addition to distributing the original version as free software. This technique has been used as a business model by a number of free software companies; this does not restrict any of the rights granted to the users of the copyleft version.
Like all free software, these projects distribute their programs under licenses that grant users all the freedoms discussed above, but because of technicalities in the licenses, combining programs by mixing source code or directly linking binaries may be problematic unless both applications are under mutually compatible licenses. When programs are not directly linked together into a single program, these problems do not exist. Much free software can run on non-free platforms such as Microsoft Windows, and non-free software can be run on free platforms, although purists prefer to use all-free software running on a free platform such as Linux.
Free software packages constitute a software ecosystem where different pieces of software can provide services to one another, leading to co-evolution of features: in one simple example, the Python programming language provides support for the HTTP protocol, and the Apache web server that provides the HTTP protocol can call the Python programming language to serve dynamic content.
The Debian Project, which produces an operating system entirely composed of free software, created a set of guidelines that are used to evaluate the compatibility of a license with Debian's free-ness goal. The Debian Free Software Guidelines are used to delineate the free from non-free software. Debian had by 2003 collected over seven and a half thousand software packages compliant with the above guidelines.
The Open Source movement is philosophically distinct from the free software movement. It was created in 1998 by a group of people, notably Eric S. Raymond, Bruce Perens, and Christine Peterson who formed the Open Source Initiative (OSI). They sought (1) to bring a higher profile to the practical benefits of sharing software source code, and (2) to interest major software houses and other high-tech industry companies in the concept. These advocates see the term open source as avoiding the ambiguity of the English word "free" in free software. The term "open source" was coined by Christine Peterson of the Foresight Institute think tank. It was registered to act as a trade mark for free software products.
Many people recognise a qualitative benefit to the software development process when a program's source code can be used, modified and redistributed by developers. (See alsoThe Cathedral and the Bazaar.) The free software movement places primary emphasis on the moral or ethical aspects of software, seeing technical excellence as a desirable by-product of its ethical standard. The Open Source movement sees technical excellence as the primary goal, regarding source code sharing as a means to an end. As such, the FSF distances itself both from the Open Source movement and from the term "Open Source".
Since the OSI only approves free software licenses as complying with the OSD, most people interpret it as a distribution scheme, and freely interchange "open source" with "free software". Even though there are important philosophical differences between the two terms, particularly in terms of the motivations for developing and using such software, they seldom make any impact in the collaboration process.
Whilst the term "Open Source" removes the ambiguity of Freedom versus Price, it introduces another: between programs that meet the Open Source Definition, giving users the freedom to improve upon them, and programs that simply have source available, possibly with heavy restrictions on the use of that source. Many people believe that any software that has source available is open source because they can tinker with it themselves. However, much of this software does not give its users the freedom to distribute their modifications, restricts commercial usage, or otherwise restricts users' rights.
Since free software allows free use, modification, and distribution, it often finds a home in third world countries for whom the cost of proprietary software is sometimes prohibitive. It is also easily modified locally, so translation efforts into languages which are not necessarily commercially profitable are also feasible. See also internationalization.
Most free software is produced by international teams cooperating through free association. Teams typically are composed of individuals with a wide variety of motivations. There are many stances about the relation of free software to the current, capitalist economic system:
Some consider free software to be a competitor to capitalism.
Some consider free software to be another form of competition within free markets, and that copyright is a governmental restriction on the market.
Groups like Oekonux and Hipatia consider that everything could be produced in this manner and that this mode of production has the potential to supersede the capitalist mode of production.
Freeware, software that can be distributed and used without cost. Few strings are attached; sometimes only private, non-commercial use is allowed. The software may not be modified, and sometimes may also not be redistributed.
Adware, software which displays advertisements during use. Legit adware is often a kind of shareware which may be used for free with ads, other adware is a kind of spyware which comes with advertising. This second kind is often installed without the consent of the installee.
Crippleware, software which can be used in a limited form for free; the enhanced version typically requires payment (see shareware).
The following are freely available to a greater or lesser degree, but are not properly "free software" in this sense:
Shareware's license requires payment for use beyond a specified trial period. The payment typically has to be made by the user on an "honor system".
Warez is current proprietary software which is distributed for free by a third party in violation of its copyright license.
Abandonware is software which is used and distributed in violation of copyright license, like warez, but is no longer sold or developed by its owner. Its copyright may or may not be enforced by the owner.