Free-software license
A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and redistribute that software. These actions are usually prohibited by copyright law, but the rights-holder of a piece of software can remove these restrictions by accompanying the software with a software license which grants the recipient these rights. Software using such a license is free software as conferred by the copyright holder. Free-software licenses are applied to software in source code and also binary object-code form, as the copyright law recognizes both forms.
Comparison
| Public domain & equivalents | Permissive license | Copyleft | Noncommercial license | Proprietary license | Trade secret | |
| Description | Grants all rights | Grants use rights, including right to relicense | Grants use rights, forbids proprietization | Grants rights for noncommercial use only. May be combined with copyleft. | Traditional use of copyright; no rights need to be granted | No information is made public |
| Software | Unlicense | MIT, Apache | GPL, AGPL, LGPL, MPL | JRL, AFPL | proprietary software, no public license | private, internal software |
| Other creative works | PD, CC0 | CC BY | CC BY-SA | CC BY-NC | Copyright, no public license | unpublished |
Free-software licenses provide risk mitigation against different legal threats or behaviors that are seen as potentially harmful by developers:
| AGPLv3 | GPLv3 | GPLv2 | LGPLv3 | LGPLv2.1 | MPLv2 | Apache-2.0 | BSD | |
| SaaS/cloud | ||||||||
| Tivoization | ||||||||
| Patent trolling | ||||||||
| Proprietization | ||||||||
| Granularity | Project | Project | Project | Library | Library | File | ||
| Trademark grant |
History
Pre-1980s
In the early times of software, sharing of software and source code was common in certain communities, for instance academic institutions.Before the US Commission on New Technological Uses of Copyrighted Works decided in 1974 that "computer programs, to the extent that they embody an author's original creation, are proper subject matter of copyright", software was not considered copyrightable. Therefore, software had no licenses attached and was shared as public-domain software. The CONTU decision plus court decisions such as Apple v. Franklin in 1983 for object code, clarified that the Copyright Act gave computer programs the copyright status of literary works and started the licensing of software.
Free-software licenses before the late 1980s were generally informal notices written by the developers themselves. These early licenses were of the "permissive" kind.
1980s
In the mid-1980s, the GNU project produced copyleft free-software licenses for each of its software packages. An early such license was used for GNU Emacs in 1985, which was revised into the "GNU Emacs General Public License" in late 1985, and clarified in March 1987 and February 1988. Likewise, the similar GCC General Public License was applied to the GNU Compiler Collection, which was initially published in 1987. The original BSD license is also one of the first free-software licenses, dating to 1988. In 1989, version1 of the GNU General Public License was published. Version2 of the GPL, released in 1991, went on to become the most widely used free-software license.1990s to 2000s
Starting in the mid-1990s and until the mid-2000s, the open-source movement pushed and focused the free-software idea forward in the wider public and business perception. In the Dot-com bubble time, Netscape Communications' step to release its webbrowser under a FOSS license in 1998, inspired many other companies to adapt to the FOSS ecosystem. In this trend companies and new projects wrote their own FOSS licenses, or adapted existing licenses. This License proliferation was later recognized as problem for the Free and open-source ecosystem due to the increased complexity of license compatibility considerations. While the creation of new licenses slowed down later, license proliferation and its impact are considered an ongoing serious challenge for the free and open-source ecosystem.From the free-software licenses, the GNU GPL version2 has been tested in to court, first in Germany in 2004 and later in the US. In the German case the judge did not explicitly discuss the validity of the GPL's clauses but accepted that the GPL had to be adhered to: "If the GPL were not agreed upon by the parties, defendant would notwithstanding lack the necessary rights to copy, distribute, and make the software 'netfilter/iptables' publicly available." Because the defendant did not comply with the GPL, it had to cease use of the software. The US case was settled before a verdict was arrived at, but at an initial hearing, Judge Saris "saw no reason" that the GPL would not be enforceable.
Around 2004 lawyer Lawrence Rosen argued in the essay Why the public domain isn't a license software could not truly be waived into public domain and can't be interpreted as very permissive FOSS license, a position which faced opposition by Daniel J. Bernstein and others. In 2012 the dispute was finally resolved when Rosen accepted the CC0 as open source license, while admitting that contrary to his previous claims copyright can be waived away, backed by Ninth circuit decisions.
In 2007, after years of draft discussion, the GPLv3 as major update of the GPLv2 was released. The release was controversial due to the significant extended scope of the license, which made it incompatible with the GPLv2. Several major FOSS projects decided against adopting the GPLv3.
On the other hand, in 2009, two years after the release of the GPLv3, Google open-source programs office manager Chris DiBona reported that the number of open-source projects licensed software that had moved to GPLv3 from GPLv2 was 50%, counting the projects hosted at Google Code.
2010s
In 2011, four years after the release of the GPLv3, 6.5% of all open-source licensed projects were GPLv3 while 42.5% were still GPLv2 according to Black Duck Software data. Following in 2011 451 Group analyst Matthew Aslett argued in a blog post that copyleft licenses went into decline and permissive licenses increased, based on statistics from Black Duck Software.In 2015 according to Black Duck Software and GitHub statistics, the permissive MIT license dethroned the GPLv2 as most popular free-software license to the second place while the permissive Apache license follows already at third place. In June 2016 an analysis of Fedora Project's packages revealed as most used licenses the GPL, MIT, BSD, and the LGPL.
Definitions
OSI-approved open-source licenses
The group Open Source Initiative defines and maintains a list of approved open-source licenses. OSI agrees with FSF on all widely used free-software licenses, but differ from FSF's list, as it approves against the Open Source Definition rather than the Free Software Definition. It considers Free Software Permissive license group to be a reference implementation of a Free Software license. Thus its requirements for approving licenses are different.FSF-approved free-software licenses
The Free Software Foundation, the group that maintains the Free Software Definition, maintains a non-exhaustive list of free-software licences.The Free Software Foundation prefers copyleft free-software licensing rather than permissive free-software licensing for most purposes. Its list distinguishes between free-software licenses that are compatible or incompatible with the FSF's copyleft GNU General Public License.
Conditions in free-software licenses
There exists an ongoing debate within the free-software community regarding the fine line between what restrictions can be applied and still be called "free".Only "public-domain software" and software under a public-domain-like license is restriction-free. Examples of public-domain-like licenses are, for instance, the WTFPL and the CC0 license. Permissive licenses might carry small obligations like attribution of the author but allow practically all code use cases. Certain licenses, namely the copyleft licenses, include intentionally stronger restrictions in order to force derived projects to guarantee specific rights which can't be taken away.
Copyleft
The free-software share-alike licenses written by Richard Stallman in the mid-1980s pioneered a concept known as "copyleft". Ensuing copyleft provisions stated that when modified versions of free software are distributed, they must be distributed under the same terms as the original software. Hence they are referred to as "share and share alike" or "quid pro quo". This results in the new software being open source as well. Since copyleft ensures that later generations of the software grant the freedom to modify the code, this is "free software". Non-copyleft licenses do not ensure that later generations of the software will remain free.Developers who use GPL code in their product must make the source code available to anyone when they share or sell the object code. In this case, the source code must also contain any changes the developers may have made. If GPL code is used but not shared or sold, the code is not required to be made available and any changes may remain private. This permits developers and organizations to use and modify GPL code for private purposes without being required to make their changes available to the public.
Supporters of GPL claim that by mandating that derivative works remain under the GPL, it fosters the growth of free software and requires equal participation by all users. Opponents of GPL claim that "no license can guarantee future software availability" and that the disadvantages of GPL outweigh its advantages. Some also argue that restricting distribution makes the license less free. Whereas proponents would argue that not preserving freedom during distribution would make it less free. For example, a non-copyleft license does not grant the author the freedom to see modified versions of his or her work if it gets publicly published, whereas a copyleft license does grant that freedom.