Software Licenses, Free and Open Source Software Péter Jeszenszky Faculty of Informatics, University of Debrecen [email protected] Last modified: April 16, 2020 Terminology ● Non-Free Software, Closed-Source Software, Proprietary Software ● Free Software ● Open-Source Software ● Free and Open-Source Software (FOSS) ● Commercial Software ● Freeware, Shareware ● Software License ● End-User License Agreement (EULA) ● License Compatibility ● Copyleft, Copyleft License ● Public Domain ● Dual Licensing, Multi-Licensing 2 Non-Free Software ● Non-free software is any software that is not free. – Its use, redistribution or modification is prohibited or restricted, or requires permission. – It is also called as closed source software or proprietary software. – Non-free software is the complementary set of free software. 3 Free Software ● The four essential freedoms: – The freedom to run the program for any purpose. – The freedom to study how the program works. – The freedom to redistribute copies of the program. – The freedom to modify the program. ● Access to the source code is a precondition for the second and the fourth freedom. ● See: The Free Software Definition https://www.gnu.org/philosophy/free-sw.html.en 4 Open Source Software (1) ● The terms “free software” and “open source software” refer to almost the same range of software. However, they represent two different approaches. – Definition: The Open Source Definition https://opensource.org/docs/osd ● The term “open source” is more suitable for marketing purposes than the “term free” software. – Free is an ambiguous word. One meaning of the word is “at no cost”. ● See, for example, “free speech” vs “free beer”. 5 Open Source Software (2) ● The free software movement emphasizes the ethical aspects of freedom. ● By contrast, the open source movement emphasizes the practical advantages of openness. ● Despite the ideological differences between the two camps, the terms free software and open source software practically have the same meaning. 6 Open Source Software (3) ● Open Source Initiative (OSI) https://opensource.org/ – A non-profit organization founded 1998 to promote and support open source software. – Eric S. Raymond, a leading advocate of the open source movement, was its president until 2005. 7 Open Source Software (4) ● See also: – Richard Stallman. Why Open Source misses the point of Free Software. https://www.gnu.org/philosophy/open-source-misse s-the-point.html – Eric S. Raymond. The Cathedral and the Bazaar. February 18, 2010. http://www.catb.org/esr/writings/cathedral-bazaar/ 8 Alternative Name ● Free and Open-Source Software (FOSS) – A category that includes both free software and open source software. – Also known as: Free/Libre and Open-Source Software (FLOSS). ● See also: Richard Stallman. FLOSS and FOSS. https://www.gnu.org/philosophy/floss-and-foss.h tml 9 Commercial Software ● Commercial software is software developed by a business as part of its business. ● Most commercial software is proprietary, but there is commercial free software. ● See: Categories of Free and Nonfree Software – Commercial software https://www.gnu.org/philosophy/categories.html #commercialSoftware 10 Freeware, shareware ● Freeware: – The term “freeware” has no clear accepted definition. – It is commonly used for packages which permit redistribution but not modification (and their source code is not available). – Freeware is not free software. – See: Categories of Free and Nonfree Software – Freeware https://www.gnu.org/philosophy/categories.html#freeware ● Shareware: – 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. – See: Categories of Free and Nonfree Software – Shareware https://www.gnu.org/philosophy/categories.html#shareware 11 Software License ● A software license is a legal instrument that regulates the distribution and use of software. – In the case of proprietary software, the term end- user license agreement (EULA) is used. 12 License Compatibility ● We say that several licenses are compatible if there is a way to merge code under those various licenses while complying with all of them. – See: Richard Stallman. License Compatibility and Relicensing. https://www.gnu.org/licenses/license-compatibility.ht ml 13 FOSS Licenses (1) ● Numerous FOSS licenses exist. – For example, the OSI maintains of list of approved open source licenses: Licenses & Standards https://opensource.org/licenses – Another useful source: Various Licenses and Comments about Them https://www.gnu.org/licenses/license-list.html 14 FOSS Licenses (2) ● The lists of FOSS licenses approved by the FSF and the OSI include all widely used software licenses. – For example, the NASA Open Source Agreement v1.3 is an OSI-approved open source license, however, the FSF does not consider it to be a free software license. ● See: – https://opensource.org/licenses/NASA-1.3 – Various Licenses and Comments about Them – NASA Open Source Agreement https://www.gnu.org/licenses/license-list.html#NASA 15 Permissive Software Licenses (1) ● Permissive licenses constitute a subset of FOSS licenses. ● These licenses permit almost any use of the code. – See: Categories of Free and Nonfree Software – Lax Permissive Licensed Software https://www.gnu.org/philosophy/categories.html#LaxPe rmissiveLicensedSoftware ● Also known as: non-copyleft licenses. – See: Open Source Initiative – Frequently Answered Questions https://opensource.org/faq#permissive 16 Permissive Software Licenses (2) ● Examples: – Apache License 2.0 https://www.apache.org/licenses/LICENSE-2.0 – BSD license: ● 3-Clause BSD License/New BSD License/Modified BSD License https://opensource.org/licenses/BSD-3-Clause ● 2-Clause BSD License (Simplified BSD License/FreeBSD License) https://www.freebsd.org/copyright/freebsd-license.html – X11 License (MIT License) https://opensource.org/licenses/MIT 17 Permissive Software Licenses (3) ● Each license mentioned here permits software distributed under it to be used for closed source software projects. – Including modification of the source code and incorporating the original or the modified source code into proprietary software. 18 Permissive Software Licenses (4) ● Examples of uses: – Apache Maven (license: Apache License 2.0) https://www.apache.org/licenses/ – FreeBSD (license: FreeBSD License) https://www.freebsd.org/copyright/freebsd-license.html – Gradle (license: Apache License 2.0) https://gradle.org/license/ – HSQLDB (license: 3-clause BSD license) http://hsqldb.org/web/hsqlLicense.html – MINIX 3 (license: MINIX 3 License) http://www.minix3.org/doc/faq.html#legal – PostgreSQL (license: PostgreSQL License) https://www.postgresql.org/about/licence/ – … 19 Copyleft (1) ● The term copyleft is a twist on the term copyright. ● Copyleft is a legal instrument whose goal is the exact opposite of that of the copyright. ● The idea was invented by Richard Stallman in 1985. ● Definition: What is Copyleft https://www.gnu.org/copyleft/ 20 Copyleft (2) ● Symbol: – Source: Wikimedia Commons / Public Domain https://commons.wikimedia.org/wiki/File:Copyleft.sv g 21 Copyleft (3) ● The copyleft ensures that the protected work and any derivative works remain free forever. – When the copyleft is in effect, then all derivative works inherit the license of the original work. ● It was first used in the Emacs General Public License. – See: http://www.free-soft.org/gpl_history/emacs_gpl.html ● Not all free software licenses incorporate the copyleft mechanism. 22 Copyleft Licenses (1) ● Software licenses using the copyleft mechanism are called copyleft licenses. – They are also called as viral licenses, pejoratively. ● Copyleft licenses represent a subset of FOSS licenses that is disjoint with the set of permissive licenses. ● Copyleft licenses are further divided into strong and weak copyleft licenses. 23 Copyleft Licenses (2) ● Strong copyleft license: the copyleft applies with full force, that excludes the use of the software covered by the license for developing closed source software. – Example: GNU General Public License (GNU GPL) https://www.gnu.org/licenses/gpl.html ● Weak copyleft license: they permit the limited use of the software covered by the license such that derivative works do not fall under the copyleft. – Examples: ● GNU Lesser General Public License (GNU LGPL) https://www.gnu.org/licenses/lgpl.html ● Mozilla Public License (MPL) https://www.mozilla.org/MPL/ 24 GNU General Public License (GNU GPL) ● The latest version is version 3. https://www.gnu.org/licenses/gpl-3.0.html ● Examples of uses: – GIMP (license: GPLv3) https://www.gimp.org/about/COPYING – Linux Kernel (license: GPLv2) https://www.kernel.org/pub/linux/kernel/COPYING – Notepad++ (license: GPLv2) https://github.com/notepad-plus-plus/notepad-plus-plus/blob/master/LICENS E – R (license: GPLv2 or GPLv3) https://www.r-project.org/Licenses/ – VirtualBox (license: GPLv2) https://www.virtualbox.org/wiki/Licensing_FAQ – VLC (license: GPLv2) http://www.videolan.org/legal.html – … 25 Using GPL-Covered Software (1) ● Copyleft licenses impose limitations on the distribution of derivative works that are unacceptable for developing non-free software. ● However, they do not limit the use of the software itself. ● Example: Blender https://www.blender.org/ – It is distributed under the GPLv3. The program can be used for developing non-free software, the license does not apply to the artworks created by the program. – See: https://www.blender.org/about/license/