Free software

Free software is defined by the freedoms granted to its users, not by whether the software costs money. The Free Software Foundation identifies four essential freedoms: to run the program for any purpose; to study how it works; to redistribute copies; and to distribute modified versions.¹

Access to source code is necessary for studying and changing most programs, so a free-software license must make that code available in a usable form. These freedoms apply to individuals, organizations, and fields of activity without discrimination. A developer may charge for distribution, support, hosting, customization, or warranty services; the license’s central requirement is that recipients retain the relevant freedoms.

Free software therefore differs from freeware, which is usually available at no monetary cost but may remain proprietary. It also differs from merely “open code” if the legal permissions do not allow independent redistribution or modification.

The modern free-software movement emerged from concerns about users losing the ability to inspect and share the programs on which they depended. In 1983, Richard Stallman announced the GNU Project, an effort to develop a Unix-compatible operating system composed entirely of software respecting these freedoms.²

Licenses supply the legal mechanism. The GNU General Public License (GPL) permits use, study, modification, and redistribution, while requiring distributed modified versions to preserve the same freedoms under specified conditions.³ This approach is known as copyleft: copyright law is used to require continued sharing rather than to prohibit copying.

Not every free-software license is copyleft. Permissive licenses, including the MIT and BSD families, generally allow modified versions to be redistributed under more restrictive terms, provided their notice and attribution conditions are met.

Free software is developed through a mixture of volunteer work, institutional sponsorship, paid engineering, and commercial services. Projects may be coordinated by foundations, companies, universities, or informal communities; their governance ranges from individual maintainers to elected or chartered bodies.

Debian, for example, makes software freedom a central principle in its social contract and packaging policies.⁴ The Linux kernel is another prominent example: it is distributed under the GPL version 2 and is developed by a global network of contributors and firms.

The phrase open source arose in the late 1990s as a related description emphasizing practical development advantages such as peer review and collaborative improvement. The Open Source Definition overlaps substantially with free-software licensing requirements, although the two movements differ in historical emphasis and rhetoric.⁵

Freedom to modify software does not guarantee that every modification can be distributed under the same name. Projects may reserve trademarks, require preservation of notices, or impose technical conditions for conveying source code. These rules can coexist with software freedom because they regulate branding or distribution obligations rather than the core permission to study and change code.

Free software also includes infrastructure that users rarely see, such as compilers, libraries, firmware tools, documentation, build systems, and accessibility utilities. A program can be licensed freely yet remain difficult to alter if its build process, dependencies, or hardware interfaces are unavailable; practical control therefore depends on more than a source-code archive.

Some licenses are incompatible with one another, making it impossible to combine particular codebases in a single distributed work without relicensing or architectural separation. Security practices likewise require care: public source code enables inspection, but it does not by itself ensure that vulnerabilities will be found or repaired.

Copyleft

A licensing approach that uses copyright law to require certain redistributed modified versions to remain available under compatible freedom-preserving terms.

Source code

The human-readable form of a program from which executable software can be built or whose logic can be studied and changed.

Permissive license

A free-software license that generally allows redistribution under modified licensing terms, subject to conditions such as preserving notices.

Freeware

Software distributed without a purchase price, but not necessarily with the freedoms to study, modify, or redistribute it.