Comparison of popular software licenses.

For all licenses, you cannot go back: once a given software version is published with a license, that license is valid for good.

You can however allow multiple licences so that users may chose which one they will use.

Some licenses are called dual X/Y (e.g.: dual BSD/GPL), meaning that users can chose between them.

• you can use, study, share (copy), and modify the software

• you are not obliged to open source your modifications

• every substantial reproduction of the software must maintain the copyright note

Basically like GPL except you can use in commercial projects, so you can basically do anything you want, except remove the license from sub products

TODO vs MIT

https://en.wikipedia.org/wiki/ISC_license

If someone else makes a derivative work of your code and distributes it, he must make the source open.

What counts as a "derivative" is gray. Some well known cases that count as derivative:

• modify the source
• use the source in your project, even if you don't modify it
• use compiled output like .so in your project. The LGPL exists to allow that.

Things which do not count as derivatives:

• Linux kernel specifics, Kernels are atypical softwares, and the following rules apply to Linux:

  • systems calls do not count as derivatives: https://github.com/torvalds/linux/blob/v4.4/COPYING#L2
  • loadable modules do not count as derivatives: http://unix.stackexchange.com/questions/13284/proprietary-or-closed-parts-of-the-kernel http://stackoverflow.com/questions/2721290/propietary-modules-within-gpl-and-bsd-kernels

Apple Store and GPL:

• https://www.fsf.org/news/2010-05-app-store-compliance
• http://www.fsf.org/blogs/licensing/more-about-the-app-store-gpl-enforcement

The holder of the copyright is not force to do so. For example, before being bought by Oracle, MySQL makers got some money from selling licences that allows companies to distribute closed source forks of MySQL.

By default, everyone owns whichever modifications they make. So if someone makes something and then merges back, you cannot not sell a relicensed version without asking for their permission.

I think it is because of this that you don't write your name on the GPL, e.g. unlike MIT. Otherwise, every derived work would say it is owned by you. TODO but then, how do you get attribution? http://programmers.stackexchange.com/questions/170188/is-requiring-attribution-gpl-compatible

If you don't distribute the code, you can fork it without opening the source: http://stackoverflow.com/questions/1492687/using-gpl-3rd-party-code-for-internal-closed-source-project Of course, what "distributing" mans may be blurry: http://programmers.stackexchange.com/questions/162870/gpl-what-is-distribution

You are not forced to merge back: only open source the contributions. But in the end it is much more profitable to try to merge back, as the community will then maintain the code for you.

You are obliged to give away the method used to generate the derivative work, e.g. the Makefile. TODO: what if it requires a closed source compiler? This site says no: https://softwarefreedom.org/resources/2008/compliance-guide.html, you only need to say what version of it you used, and how.

The following website is of a leading group of lawyers that enforces GPL: http://gpl-violations.org/about.html It is in general up to the copyright owner to enforce GPL.

Notable cases include:

• Iliad: major Telecom player in France, sued in 2008, released it's source code modification in 2011 at http://floss.freebox.fr to avoid further pursuits.

It is also helpful to see what they have to say about other projects: http://www.gnu.org/licenses/license-list.en.html

It is not very clear in the GPL text is dynamic and static linking are allowed or not from proprietary libraries.

It is therefore better to play it safe and assume that it is not possible.

libgit2 is a notable example of GPLv2 with a linking exception, explicitly allowing linking, since GitHub is behind the library.

E.g. Python import:

• https://softwareengineering.stackexchange.com/questions/87446/using-a-gplv3-python-module-will-my-entire-project-have-to-be-gplv3-licensed
• https://opensource.stackexchange.com/questions/1487/how-does-the-gpls-linking-restriction-apply-when-using-a-proprietary-library-wi
• https://opensource.stackexchange.com/questions/2139/can-i-license-python-project-under-3-clause-bsd-while-it-has-gpl-based-dependenc
• https://stackoverflow.com/questions/999468/question-on-importing-a-gpled-python-library-in-commercial-code
• https://softwareengineering.stackexchange.com/questions/167773/how-does-the-gpl-static-vs-dynamic-linking-rule-apply-to-interpreted-languages
• https://en.wikipedia.org/wiki/Python_Software_Foundation_License

A company A cannot modify a GPL source, and license it to another company B, with a license that requires the other company B to not release the source it received.

http://en.wikipedia.org/wiki/GNU_Lesser_General_Public_License

Lesser GPL: closed source projects can use it without opening their source, but they must allow end users to modify the LGPL component.

Quintessential example: glibc. Every C program links to it. So if it were GPL, there could be no closed source C programs on Linux, which would be too restrictive.

For this reason, this license is used in practice mostly for linked libraries where the separation between library and proprietary code is clear.

LGPL 2.1 was standalone, with not relation to GPL. LGPL 3 refer to the GPL: https://en.wikipedia.org/wiki/GPL_linking_exception

http://www.gnu.org/licenses/fdl-1.3.en.html

https://en.wikipedia.org/wiki/GNU_Free_Documentation_License

See also: Creative Commons.

Used by Wikipedia, dual with CC BY SA.

GPL allows you to modify software used Server Side without distributing the source code.

Affero GPL blocks it:

• http://programmers.stackexchange.com/questions/131264/what-constitutes-distributing-for-lgpl-v3
• http://www.gnu.org/licenses/why-affero-gpl.en.html

Apparently you can use AGPL as a service in the backend of a closed source site: what you can't do is make source level usage / modifications to it.

MongoDB uses it: http://programmers.stackexchange.com/questions/226111/can-i-use-mongodb-for-a-commercial-web-based-service But it explicitly notes that you can use it as a backend for closed source projects.

MySQL Google closed source fork is a notable case where the server-side loophole was used.

Banned by Google: http://www.theregister.co.uk/2011/03/31/google_on_open_source_licenses/

Family of licenses.

https://creativecommons.org/licenses/

https://wiki.creativecommons.org/Frequently_Asked_Questions

Not specialized for software, and more used for human readable text, music, etc.

Likely the best choice for non-software. One main reason is that it is very popular, so using it makes it much easier to interface with other projects.

One major downside for text is that it does not require source code to be released: http://programmers.stackexchange.com/questions/297894/does-the-creative-commons-sharealike-license-require-that-source-code-of-derivat

Used by: Stack Overflow and Wikipedia (BY_SA) content.

The main difference between software and text is that for text the source is easily derived from the human readable output. Software however can be useful in a form that is not human understandable through compiled code.

For media like music, there may not even be a source format.

You can combine the following options as you wish:

• BY: attribution to creator. All combinations have this, otherwise you cannot know who holds the rights.

• SA: shared material and adaptations must have the same license.

• ND: no derive: can't modify and share, but can modify and use internally.

  This is even more restrictive than GPL, which allows sharing as long as the source is distributed.

• NC: cannot use in commercial products.

  This has many gray zones.

  In particular, I cannot find if you can make internal usage in a enterprise.

  https://creativecommons.org/weblog/entry/17127

and many fixed combinations are possible.

This is indicated in their logo.

What CC can you combine: https://wiki.creativecommons.org/wiki/Frequently_Asked_Questions#Can_I_combine_material_under_different_Creative_Commons_licenses_in_my_work.3F

Creative commons public domain version. GPL compatible.

Term that can be used to describe several licenses, and I think it has legal meaning in different countries. Those licenses include CC0.

You relinquish your copyright. You are not the copyright owner anymore.

Once released on the public domain, you relinquish any rights you have over the work: in particular you cannot change it to another license later on.

Anyone can do anything with the work without even mentioning you, except copyright it.

There have been cases of removal from the public domain because of earlier international blunders: http://www.themarysue.com/take-works-out-of-public-domain/

There are some practical downsides of public domain licences: http://linuxmafia.com/faq/Licensing_and_Law/public-domain.html

http://programmers.stackexchange.com/questions/182137/whats-the-difference-between-wtfpl-cc0-and-public-domain

TODO.

It seems that by default in all licenses, the person who makes a significant change owns it.

So if you want to sell a relicensed version, you'd have to contact everyone.

This is why the FSF requires software assignments for merging back. This is a great idea.

TODO: is there a license that requires assignment automatically on commit? http://programmers.stackexchange.com/questions/191535/could-submitting-a-pull-request-ever-constitute-accepting-a-contributor-licence

Examples:

• http://apache.org/licenses/icla.txt
• https://cla.developers.google.com/about/google-individual
• http://doc.gitlab.com/ce/legal/individual_contributor_license_agreement.html

GitHub: https://github.com/clahub/clahub But I think I'd just keep it inside the repo in a CLI.md file, and make first time committers write a line there saying I agree.

TODO: can you make a CLA that allows you to resell the work under a different license? E.g.: you work is GPL, someone contributes, and then you want to sell a license that allows buyers to modify the source, without asking every single contributor if you can do that with their code. Discourse's makes that very clear with: the terms "relicense".

Stronger than CLA: gives copyright to someone else.

http://producingoss.com/en/copyright-assignment.html vs CLA Contributor License Agreement

Used by the FSF.

https://en.wikipedia.org/wiki/Freedom_of_panorama

https://commons.wikimedia.org/wiki/Commons:Freedom_of_panorama

Mozilla Public License.

https://en.wikipedia.org/wiki/Mozilla_Public_License

Per-file GPL.

Version 2 GPL compatible.

Common Development and Distribution License.

https://en.wikipedia.org/wiki/Common_Development_and_Distribution_License

Similar to Mozilla, but not GPL compatible: http://vschart.com/compare/mozilla-public-license/vs/common-development-and-distribution-license

• freeware: currently free to use
• shareware: https://en.wikipedia.org/wiki/Shareware

https://en.wikipedia.org/wiki/SIL_Open_Font_License

Most popular license at fontlibrary.org: https://fontlibrary.org/en/search?license=OFL%20%28SIL%20Open%20Font%20License%29

This is what as decided on the Oracle v. Google case:

• http://law.stackexchange.com/questions/10945/would-the-oracle-v-google-lawsuit-imply-that-any-api-can-be-re-implemented-inc/10950#10950
• http://law.stackexchange.com/questions/7683/in-the-us-when-is-fair-use-a-defense-to-copyright-infringement/7684#7684
• http://law.stackexchange.com/questions/9510/in-oracle-america-v-google-what-was-the-district-court-jurys-rationale-behind

It basically give very little insight into future similar cases.

Can enforce anything that is not illegal. Some cool examples:

• you cannot disclose benchmarks of this product. So how can you compare between two vendors? You have to buy both!
  • http://law.stackexchange.com/questions/7272/is-the-benchmarking-clause-in-vmwares-eula-actually-valid
  • Cadence goes a step further and forbids internal benchmarks as well: https://web.archive.org/web/20161008212948/https://www.sec.gov/Archives/edgar/data/1160958/000119312511056594/dex1014.htm
• You cannot use this as legal evidence against us:

  Your access to the information in this ARM Architecture Reference Manual is conditional upon your acceptance that you will not use or permit others to use the information for the purposes of determining whether implementations of the ARM architecture infringe any third party patents. Very practical. Just put that note on everything you make, and you can never be sued! How can this be enforceable.

Enforceability:

• http://superuser.com/questions/30940/is-an-eula-enforceable
• https://en.wikipedia.org/wiki/End-user_license_agreement#Enforceability_of_EULAs_in_the_United_States
• https://www.eff.org/wp/dangerous-terms-users-guide-eulas Mentions the non-benchmark EULA.

https://en.wikipedia.org/wiki/Free_Art_License

A copyleft for art.