Categories of Free and Non-Free Software

Here is a glossary of various categories of software that are often mentioned in discussions of free software. It explains which categories overlap or are part of other categories.

Other texts to read | ``Free software'' | ``Public domain software'' | ``Copylefted software'' | ``Non-copylefted free software'' | ``GPL-covered software'' | ``The GNU system'' | ``GNU software'' | ``Semi-free software'' | ``Proprietary software'' | ``Shareware'' | Other texts to read

Also note Confusing Words which You Might Want to Avoid.

Free software
Free software is software that comes with permission for anyone to use, copy, distribute, and modify (including distribution of modified versions). In particular, this means that source code is available; it also means that for-profit companies can distribute copies for a fee.

If a program is free, then it can potentially be included in a free operating system such as GNU.

There are many different ways to make a program free---many questions of detail, which could be decided in more than one way and still make the program free. Some of the possible variations are described below.

Free software is a matter of freedom, not price. But proprietary software companies sometimes use the term ``free software'' to refer to price. Sometimes they mean that you can obtain a binary copy at no charge; sometimes they mean that a copy is included on a computer that you are buying. This has nothing to do with what we mean by free software in the GNU project.

Because of this potential confusion, when a software company says its product is free software, always check the actual distribution terms to see whether users really have all the freedoms that free software implies. Sometimes it really is free software; sometimes it isn't.

Many languages have two separate words for ``free'' as in freedom and ``free'' as in zero price. For example, French has ``libre'' and ``gratuit''. English has a word ``gratis'' that refers unambiguously to price, but no common adjective that refers unambiguously to freedom. This is unfortunate, because such a word would be useful here.

Public domain software
Public domain software is software that is not copyrighted. It is a special case of non-copylefted free software, which means that some copies or modified versions may not be free at all. Sometimes people use the term ``public domain'' in a loose fashion to mean ``free'' or ``available gratis.'' However, ``public domain'' is a legal term and means, precisely, ``not copyrighted''. For clarity, we recommend using ``public domain'' for that meaning only, and using other terms to convey the other meanings.

Copylefted software
Copylefted software is free software whose distribution terms do not let redistributors add any additional restrictions when they redistribute or modify the software. This means that every copy of the software, even if it has been modified, must be free software.

In the GNU Project, we copyleft almost all the software we write, because our goal is to give every user the freedoms implied by the term ``free software.'' See Copylefted for more explanation of how copyleft works and why we use it.

Copyleft is a general concept; to actually copyleft a program, you need to use a specific set of distribution terms. There are many possible ways to write copyleft distribution terms.

Non-copylefted free software
Non-copylefted free software comes from the author with permission to redistribute and modify, and also to add additional restrictions to it.

If a program is free but not copylefted, then some copies or modified versions may not be free at all. A software company can compile the program, with or without modifications, and distribute the executable file as a proprietary software product.

The X Window System illustrates this. The X Consortium releases X11 with distribution terms that make it non-copylefted free software. If you wish, you can get a copy which has those distribution terms and is free. However, there are non-free versions as well, and there are popular workstations and PC graphics boards for which non-free versions are the only ones that work. If you are using this hardware, X11 is not free software for you.

GPL-covered software
The GNU GPL (General Public License) (20k characters) is one specific set of distribution terms for copylefting a program. The GNU Project uses it as the distribution terms for most GNU software.

The GNU system
The GNU system is a complete free Unix-like operating system.

A Unix-like operating system consists of many programs. We have been accumulating components for this system since 1984; we have not yet released ``the complete GNU system'' as a single collection because the GNU kernel is not yet ready for users.

Since the purpose of GNU is to be free, every single component in the GNU system has to be free software. They don't all have to be copylefted, however; any kind of free software is legally suitable to include if it helps meet technical goals. We can and do use non-copylefted free software such as the X Window System.

The GNU system includes all the GNU software, as well as many other packages such as X11 and TeX which are not GNU software.

GNU software
GNU software is software that is released under the auspices of the GNU Project. Some of it is written by staff of the Free Software Foundation, but most GNU software is contributed by volunteers.

Some GNU software is copyrighted by the Free Software Foundation; some is copyrighted by the contributors who wrote it.

Semi-free software
Semi-free software is software that is not free, but comes with permission for individuals to use, copy, distribute, and modify (including distribution of modified versions) for non-profit purposes. PGP is an example of a semi-free program.

It is not possible to include semi-free software in a free operating system. This is because the distribution terms for the operating system as a whole are the conjunction of the distribution terms for all the programs in it. Adding even one semi-free program to the system would restrict the whole system.

We don't use semi-free programs for the activities of the GNU Project. If there is a job that needs doing with software, then until we have a free program to do the job, we still need a free program so we can add it to the GNU system. We have to tell volunteers, ``We don't have a program yet to do this job, so we hope you will write one.''

If we ourselves were to use a non-free program to do the job, that would take away the pressure and impetus (on us, and on others who might listen to our views) to write a free one. We mustn't do that.

Proprietary software
Proprietary software is software that is not free or semi-free. Its use, redistribution or modification is prohibited, or requires you to ask for permission, or is restricted so much that you effectively can't do it freely.

The Free Software Foundation follows the rule that we cannot install any proprietary program on our computers except temporarily for the specific purpose of writing a free replacement for that very program. Aside from that, we feel there is no possible excuse for installing a proprietary program.

For example, we were able to install Unix on our computers because we were using it to write a free replacement for Unix. If we were not working on that project, we would have considered it off limits to install Unix. Nowadays, since free operating systems are available, the excuse is no longer applicable; any new computer we install must run a completely free operating system, and we are trying to replace Unix with free systems when that is possible. Eventually all our computers will run free software only.

We don't insist that users of GNU, or contributors to GNU, have to live by this rule. It is a rule we made for ourselves. We hope you will decide to follow the same rule.

Shareware is software which comes with permission for people to redistribute copies, but says that anyone who continues to use a copy is required to pay a license fee.

Shareware is not free software, or even semi-free. There are two reasons it is not:

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Updated: 20 Mar 1997 tower