Open Source

Open ≠ Free ≠ Gratis

Software has become an integrated part of life. It's everywhere, and the complexity is increasing. As developers, we're standing on the shoulders of giants. Most of the software running in our applications is written by someone else. But do you know what you're allowed to use the software for? And what your obligations are when using the software? All software has a license, which means it contains legal talk which "authorize the use, performance, or release of (something)."

10 min read


By Simen Endsjø


December 18, 2019


I aim to give an introduction to open source and licenses to make it easier for you to look into the details on your own when needed.

  • Source code available ≠ Freedom
  • What is freedom
  • History
  • Terminology and concepts
  • Short intro to some licenses

I Am Not A Lawyer (IANAL)

I Am Not A Lawyer! Don't take legal advice from strangers on the internet! Don't trust me! I'm serious! Leave now!


Believe it or not, but software licenses are much like religion. I've been called a zealot, communist, ignorant, dumb, and everything in between over this post.

So when you're talking about Open Source or licenses with people, tread softly, and don't be alarmed if someone gets very upset and starts attacking you -- much like religious debate.

Open Source Software ≠ Can use

The phrase "Open Source" has changed meaning over the last decade. It somehow became a buzzword, and suddenly everything is "Open Source" – but what does Open actually mean?

Open ≠ Gratis: We'll use the word gratis for "doesn't cost any money". Open Source software doesn't have to be gratis any more than closed source has to cost money. And gratis software doesn't have to be open source.

Open ≠ Freedom: Even though you have access to the source code, it doesn't mean you're actually allowed to use it as you please. You might be sued by just looking at the software.

Freedom ≠ Gratis: Being allowed to use something as you please still doesn't necessarily mean it has to be gratis. And being gratis doesn't mean you're allowed to use it for your needs.

Open ≠ Can Use: In short, Open Source doesn't mean you can or are allowed to use it


Free Open Source Software (FOSS)

Several projects and companies use custom licenses and modified versions of Open Source licenses. The motives for this might be many, but I suspect the primary motivation is because it might be easier to monetize, keep control, or reduce the risk of someone taking your work, making it better, and making you obsolete. Of course, purely speculations, and regardless of motivation, the loss of freedom might be problematic for the user.

When a project is released under such license, the correct term is Source Available, not Open Source, as a key of Open Source is that you should be able to use the code as you like. It will probably still be marketed as Open Source, so you need to keep a keen eye.

There are several organizations working to promote Open Source, Open Source Initiative (OSI) and Free Software Foundation (FSF) being two prominent players. While they agree on much, and OSI-approved licenses also being FSF-approved licenses, the FSF is more strict on what freedoms it requires. But remember that for the purpose of this post, OSI and FSF are good friends playing along nicely!

Free = Freedom: The Free talks about freedom to use as you like, which is only possible if the code is also open.

Free ≠ Gratis: FOSS still doesn't have to be gratis.

But to confuse the matter even further, the word Free is often misinterpreted as Gratis, and as such is sometimes used for software which restricts your freedom.

Because of this, yet another term has been coined, Free Libre Open Source Software (FLOSS). This haven't seen much widespread use yet, but give it a couple of years, and it has probably gained another meaning :)


We've talked a bit about Freedom, but haven't given a definition. Free Software Foundation defines freedom as (emphasis mine):

  • The freedom to run the program as you wish, for any purpose (freedom 0).
  • The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1).
  • The freedom to redistribute copies so you can help others (freedom 2).
  • The freedom to distribute copies of your modified versions to others (freedom 3).

There are many non-free licenses out there, which restricts one or more of these freedoms. Think about what it would mean if a library you're using restricts the rights to redistribute. Or restricts what you're allowed to do with it.

History and some useful links

I've referred to FSF and GNU several times already without giving a reason for doing so, but there are good reasons. FSF and GNU are old projects created to support freedom in software.

  • Pre 1980, nearly all software was free.
  • During the 1980s, nearly all software became proprietary, non-free, closed source.
  • Gnu's Not Unix (GNU) was founded 1984 by Richard Stallman to create a free Unix operating system (OS).
  • Free Software Foundation (FSF) was founded in 1985 to help GNU and the free software movement financially
  • The GNU/Hurd kernel (core of the OS) is not yet ready. Linus Thorvalds released the Linux kernel in 1991.
  • GNU and Linux together makes a complete and free Unix-like OS
  • The GNU/Hurd kernel (core of the OS) is not yet ready. Linus Thorvalds released the Linux kernel in 1991.
  • GNU and Linux together makes a complete and free Unix-like OS
  • Linux Libre is Linux without non-free code
  • Free Software Directory lists a lot of free software
  • Software Freedom Conservancy helps defend free software


Copyright is a central theme to licenses. It basically means the owner of the work.

"Copyright is a form of intellectual property that grants the creator of an original creative work an exclusive legal right to determine whether and under what conditions this original work may be copied and used by others, usually for a limited term of years"

No license means full copyright to those who wrote it. You cannot use it for any purpose at all as the author(s) didn't grant you any rights to the work. If you see something without a license, turn around and don't look back.

You might have seen people "licensing" work under Public Domain, but not every country accepts this definition, so using Public Domain software might be considered a breach of copyright. Do not use "Public Domain" licensed software.


In software we're standing on the shoulders of giants. Everything we do builds upon something someone else has already built. As such, we're often modifying software (often by including a library in our own code), and then distribute it as part of our own work.

"Copyleft, distinguished from copyright, is the practice of offering people the right to freely distribute copies and modified versions of a work with the stipulation that the same rights be preserved in derivative works created later"

So while you might have been granted the rights to use something, you might not have been granted the rights to distribute it or combine it with other software.

Viral licenses

There's a lot of licenses out there, and they have wildly different purposes. As such, there are situations where parts of one license will clash with parts of another license.

Several licenses require that you use the same license for derivative work, which makes the license viral – it infects your own work. Luckily, several licenses are compatible with one another, and allows you to use one license as long as your own work is one of the compatible licenses.

If you use a GPL library, you need to use a GPL compatible license for your own work. GPL is a viral license by design to make sure nobody removes a users freedom.

Multiple licenses and copyright attribution

Because of copyleft, patents etc, a lot of people might be unable to use certain licenses. To circumvent this, much software is released under several different licenses, also called dual licensing (in the case of two) or multi licensing.

Remember that copyright is given in full to the author to a work. So a contributor will have full copyright for the contributions. The project thus cannot grant someone else access to this contribution without explicit consent from the author.

Copyright is needed in order to change or upgrade a license, to distribute under other licenses, and to take legal actions against infringements. Because of this, some projects requires the authors to sign over contributions to the project/entity owning the project.

A bit about some popular licenses

There's a lot of different licenses out there. Some are more popular than others, and libraries released in 2019 often use a different license than a library released in 2009. Some are good for products, and others are good for libraries, and some licenses might be problematic to use for commercial use or proprietary code.

The following licenses are pretty common, and you should at least look at some bullet points describing them.

Lots of freedom

  • AGPL (GNU Affero General Public License)
    • Like GPL, but includes software accessed over the network
  • GPL (GNU General Public License)
    • Users are allowed to run, study, share and modify the software
    • Derivative work must also include these freedoms

For libraries

Should be quite safe, but has some demands on the user, e.g. attribution.

  • LGPL
  • Apache 2.0
  • Expat (MIT)
  • ZLIB
  • JPEG
  • BSD (3-clause / modified)

Public Domain

"Do whatever you want, but don't sue me"

  • CC0
  • Unlicence: Rather use CC0
  • Public Domain: Might not be valid in many countries – stay away


GNU defines these as non-free by various reasons (like the phrase "do good not evil", which limits use and is subjective)

  • Artistic License 1.0
  • The JSON License
  • Microsoft Shared Source License
  • Creative Commons NonCommercial
  • Creative Commons Noderivatives

What license should I choose?

When choosing the license, you have to consider the licenses of the software you're using. They probably have restrictions on what license you can choose.

GNU has a nice recommendation list:

  • Small programs/code snippets (\<300 lines): Apache 2.0
  • Libraries you want to see used (same domain as non-free libraries): Apache 2.0
  • Other libraries wher GPL is unpractical: LGPL
  • Other libraries: GPL
  • Running on servers: AGPL
  • Longer documentation: GFDL
  • Short documentation: GNU all-permissive license


Few people read licenses from cover to cover anymore as someone has done the dirty-work of categorizing the legal-talk, making it digestible for the rest of us.

Transitive licenses

It's turtles all the way down. You're responsible for transitive libraries. Do you know that no libraries of the libraries of the libraries of the libraries use a license wrongly?

If they break the rules, so do you!

Your package manager should include ways for you to find out what licenses are in use. Search for "license checker" or similar for your package manager.

Stack Overflow

Now that we've learned that licenses can both grant you rights to use something and built upon on it, what about all the snippets on the internet where there is no explicit LICENSE along with the code. Have you read the Terms And Conditions for all sites you are a member of? When you publish code on their site, do you think you have copyright, or did you check a box when signing up for the service (after reading the long legal document of course)?

You haven't ever copied code from the internet without knowing the full extend of the license?

…. Have you ever copied code from Stack Overflow? …

"requires you to release all derivative works under this same license. You must give credit to the original author of the work, state their name and the title of the original work, say that you modified the work if you did and include the attribution logo"


  • IANAL! Don't trust random legal advice from random strangers on the internet!
  • Source Available ≠ Freedom
  • Freedom ≠ Gratis
  • Use free licenses and submit your work under free licenses
  • Make contributors sign over copyright
  • Release under more than one license if necessary
  • You're probably violating licenses! Clean up your act.