Free software, as defined by the Free Software Foundation, can be used, copied, studied, modified and redistributed. Free software is sometimes referred to by other names such as Freely redistributable software (FRS) and libre software. The opposite of free software is proprietary software.
Most free software programs are distributed gratis online, and offline for marginal cost of distribution, but this is not required, and people are free to buy and sell copies for any price. Richard Stallman, founder of the Free Software Movement, coined the phrase, "free as in freedom, not as in beer" to help people remember the difference between "libre" or "freedom" software and "gratis" or "zero price" software.
The term open source software refers to a similar category of software. (Its criteria were copied in 1998 from Debian's rewrite of the definition of "free software".) As a result, nearly all open source programs are free software, but there are some exceptions.
Although the license criteria are similar, the terms "free software" and "open source" are associated with different philosophical ideas. The terms FOSS (for Free/Open-Source Software) and FLOSS (for Free/Libre/Open Source Software) are used to mention both "free software" and "open source" equally without expressing a preference. (See Open source vs. free software for more information )
"Freeware" refers to software distributed at no charge. Freeware source code may or may not be published, and the freedom to distribute modified versions may or may not be available, so much freeware is not free software.
A brief history of Free Software:
- 1960s and 1970s - software was seen as an add-on supplied by mainframe vendors to make computers useful. Thus, programmers and developers frequently freely shared their software. This was especially common in large users groups, such as DECUS, the DEC (Digital Equipment Corporation) Users Group.
- Late 1970s - companies began routinely imposing restrictions on programmers with software license agreements.
- 1983 - Richard Stallman began the GNU project, founding the Free Software Foundation (FSF) two years later . He introduced a "free software" definition and "copyleft", designed to ensure software freedom for all .
Free software licenses
According to Stallman and the FSF, "free" software licenses grant:
- 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.
 provides a list of many free software licenses. The list is necessarily incomplete, because a license need not be known to the FSF in order to provide these freedoms.
"Proprietary software" is distributed under more restrictive software licenses. Copyright law restricts modification, duplication and redistribution rights to the copyright owner; software released under a free software license rescinds most of these reserved rights.
The FSF free software definition disregards price. CDs containing free software such as 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.
Variations on free software as defined by the FSF:
- 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.
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.
Examples of free software
The amount of free software is large and increasing.
Notable free software projects:
- Operating system kernels: Linux and the BSD kernel
- GCC compilers, GDB debugger and C libraries
- Servers: BIND name server, Sendmail mail transport, Apache web server, and Samba file server
- Relational database systems: MySQL and PostgreSQL.
- Programming languages: Perl, PHP, Python, Ruby and Tcl.
- GUI related: X Window System, GNOME and KDE desktop environments.
- OpenOffice.org office suite, Mozilla web browser and the GIMP graphics editor
- Typesetting and document preparation systems TeX and LaTeX
See the Free Software Directory  for a larger list.
Much free software supports the non-free Microsoft Windows or non-free Unix platforms, and non-free software can support free platforms, although purists prefer all-free software on a free platform such as GNU/Linux.
Free software packages constitute a software ecosystem where software provides services, resulting in mutual benefit: for instance, the Apache web server handling the HTTP protocol, using mod_python to provide dynamic content.
Social significance of free software
Free software is thought to have social significance and this can be explained as follows:
Soon after free software begins circulation, it becomes available at little to no cost. When free software spreads, its utility is constant, or even increases due to network effects. Thus, free software is a pure public good rather than a private good.
Another way free software is thought to be significant to society is due to its freedoms that result in lower cost than proprietary software. Due to this fact free software is becoming popular in third world countries such as Brazil.
Furthermore, the openness of free software eases internationalization.
International cooperation through free association produces most free software. The Oekonux and Hipatia projects contend free association could produce everything. Free association is also used for wiki writing, such as Wikipedia and give-away shops.
While the politics of Free Software are unclear it is clear that it has become not only economically but also politically significant. SCO CEO Darl McBride and others have tended to characterise Free Software as communist while others maintain that its economic footprint is largely free market orientated and therefore capitalist, particularly for businesses with a services model. It is perhaps more interesting to analyse Free Software's goals - its four freedoms - in terms of positive and negative liberty. Before proceeding, it is worth noting that a computer program is inanimate and therefore not political in its own right, when we speak of the politics of Free Software we seek to understand its social effects in the larger human context.
The four freedoms are couched in positive language, simply, users are granted the "freedom to" run, modify and reproduce the software but not granted "freedom from" anything that might prevent them from doing so. This observation is flawed when free software licences are considered in contrast to the proprietary licencing alternative. Users are given the right to use software for any purpose and are therefore free from the protective clauses of proprietary licences that are designed to limit liability or increase profits for a single vendor. If users wish to employ a Free Software program to develop nuclear weapons or service the needs of 1000 colleagues then they are not prevented from doing so by contract but only be circumstances unrelated to the licence, such as local laws and computer hardware. Similarly, the freedom to modify a program and release your improvements can also be seen as protecting groups within society from external coercion by more powerful groups through the deployment of technical implementations that prevent certain kinds of communication or activity. As an example, users are granted sufficient rights that they can correct any technical flaws in the software that affect their choice of software product that they wish to use by adding features, removing incompatabilities or creating new versions with new interopability functions. It is this and related effects on the technology market that have tended to lead to a capitalist or right-wing interpretation.
Individuals within a team typically have a wide variety of motivations.
Stances on the relationship between free software and the existing capitalist economic system:
- Competition - free software and capitalism are incompatible, so more free software results in less capitalism.
- Inter-market competition - free software is a form of competition within capitalism. Copyright is governmental market restriction.
- Gift economy - status depends on gifts.
There is controversy over the security of free software vs. proprietary software (a major issue being security through obscurity). A popular relative security measurement is counting known unpatched security flaws. Generally, users of this method advise avoiding products which lack fixes for known security flaws, at least until a fix is available.
Free software controversies
The BitKeeper controversy in the free software movement illustrates the movement's major issues and points of view.
Larry McVoy invited high-profile free software projects to use BitKeeper to attract paying users. In 2002 a controversial decision was made to use BitKeeper, a proprietary software product, to develop the Linux kernel, a free software project. The excerpt below illustrates why this proved to be a major source of controversy.
- "McVoy made the program available gratis to free software developers. This did not mean it was free software for them: they were privileged not to part with their money, but they still had to part with their freedom. They gave up the fundamental freedoms that define free software: freedom to run the program as you wish for any purpose, freedom to study and change the source code as you wish, freedom to make and redistribute copies, and freedom to publish modified versions.
- The Free Software Movement has said "Think of free speech, not free beer" for 15 years. McVoy said the opposite; he invited developers to focus on the lack of monetary price, instead of on freedom. A free software activist would dismiss this suggestion, but those in our community who value technical advantage above freedom and community were susceptible to it. ...
- A free kernel, even a whole free operating system, is not sufficient to use your computer in freedom; we need free software for everything else, too. Free applications, free drivers, free BIOS: some of those projects face large obstacles -- the need to reverse engineer formats or protocols or pressure companies to document them, or to work around or face down patent threats, or to compete with a network effect. Success will require firmness and determination. A better kernel is desirable, to be sure, but not at the expense of weakening the impetus to liberate the rest of the software world."
McVoy withdrew permission for gratis use by free software projects. Many in the free software movement see the whole affair as a vindication of Richard Stallman's principled position over the more utilitarian approach of Linus Torvalds.
- Free audio software
- Free game software
- Free/Libre Open Source Software
- Free Software Foundation
- Free software licenses
- GNU General Public Licence
- GNU Project
- Open source
- Open source culture
- Open source vs. free software
- History Free Software
- The Free Software Definition - published by FSF
- FSF's list of free software licenses, including clarifications on often confused non-free licenses
- FSF/UNESCO directory of free software packages
- The GNU philosophy pages
- FSF's comparison of "Open Source" and "Free Software"
- An argument for free software (Charles Stross)
- Why Open Source Software / Free Software (OSS/FS)? Look at the Numbers! — David Wheeler's analysis of the advantages of OSS/FS by an exhaustive review of published studies, analyses, and news reports.
- Free software rated, reviewed and available for download
- Directory of free software and open source software at Framasoft's site
- Some Code to Die for. On the Birth of the Free Software Movement in 1887 — Essay by Leo Findeisen, monochrom.
- demosoftware.net — demos and documentation wiki for GNU GPL and GNU LGPL, web-based, Free Software
- Brazil: Free Software's Biggest and Best Friend
- South Korea Steps Up Linux Use in Public Sector
- WebOpenSource.com A portal dedicated for open source software community - Includes reviews, latest news, free download and more.
- Why the future of science must be in free software — An essay about the relationship between free software and science by Alessio Damato (in PDF)