Wikipedia Free and open-source (FOSS) Software Licenses
A software license is a legal instrument (usually by way of contract law, with or without printed material)
governing the use or redistribution of software.
Under United States copyright law all software is copyright protected, in source code as also object code form.
The only exception is software in the public domain.
A typical software license grants the licensee, typically an end-user, permission to use one or more copies
of software in ways where such a use would otherwise potentially constitute copyright infringement of the software
owner's exclusive rights under copyright law.
There are several organizations in the FOSS domain who give out guidelines and definitions regarding software
Free Software Foundation maintains non-exhaustive lists of software licenses following their The Free
Software Definition and licenses which the FSF considers non-free for various reasons.
The FSF distinguishes additionally between free software licenses that are compatible or incompatible with the FSF
license of choice, the copyleft GNU General Public License.
The Open Source Initiative defines a list of certified open-source licenses following their The Open Source
Also the Debian project has a list of licenses which follow their Debian Free Software Guidelines.
Free and open-source licenses are commonly classified into two categories: Those with the aim to have
minimal requirements about how the software can be redistributed (permissive licenses), and the protective
share-alike (copyleft Licenses).
An example of a copyleft free software license is the often used GNU General Public License (GPL), also the
first copyleft license.
This license is aimed at giving and protecting all users unlimited freedom to use, study, and privately modify the
software, and if the user adheres to the terms and conditions of the GPL, freedom to redistribute the software or
any modifications to it.
For instance, any modifications made and redistributed by the end-user must include the source code for these, and
the license of any derivative work must not put any additional restrictions beyond what the GPL allows.
Examples of permissive free software licenses are the BSD license and the MIT license, which give unlimited permission to use, study, and
privately modify the software, and includes only minimal requirements on redistribution.
This gives a user the permission to take the code and use it as part of closed-source software or software released
under a proprietary software license.
It was under debate some time if Public domain software and Public domain like licenses can be considered as a kind
of FOSS license.
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 therefore be interpreted as very permissive FOSS license, a position which faced opposition by Daniel J. Bernstein and
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.