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Software Licenses

This article provides some basic framing around the purpose of licenses within open source:

  • It introduces common terms used to describe software: copyright, software licenses and open source.
  • It describes the three types of open source licenses, and why an organisation needs to track the licenses it uses.
  • The work of the Open Source Initiative (OSI) in tracking different types of license.
  • How to identify at-a-glance the characteristics of a given software license.

Some Terms

By default, in many jurisdictions (e.g. the US) the author of software holds the copyright to it, granting them exclusive rights to the work. Wikipedia describes copyright as follows:

A copyright is a type of intellectual property that gives its owner the exclusive right to copy, distribute, adapt, display, and perform a creative work, usually for a limited time. The creative work may be in a literary, artistic, educational, or musical form. - Copyright, Wikipedia

In order to allow other parties to use a piece of software, the copyright holder must issue them with a license.

2. What Is A Software License?

A software license describes what the end-user of a piece of software can do with it:

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. - Software License, Wikipedia

The concept of a license applies to all software, whether it is free, open source or commercial (proprietary). For proprietary software:

The hallmark of proprietary software licenses is that the software publisher grants the use of one or more copies of software under the end-user license agreement (EULA), but ownership of those copies remains with the software publisher (hence use of the term "proprietary"). - Proprietary Software, Wikipedia

Types of Software License

The difference between proprietary software and open source software is therefore in the license.

In this section, we'll break down software licenses into open source, proprietary, other types and unlicensed.

Open Source Licenses

Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. - Open-source software, Wikipedia

Wikipedia describes three main types of open source licenses:

1. Public Domain Licenses

This where the work has been deliberately donated to the Public Domain, or copyright on it has expired:

The public domain (PD) consists of all the creative work to which no exclusive intellectual property rights apply. Those rights may have expired, been forfeited, expressly waived, or may be inapplicable. Because no one holds the exclusive rights, anyone can legally use or reference those works without permission. - Public Domain, Wikipedia

An example of a public domain license is CCO, which is a license with "no rights reserved".

2. Permissive Licenses

Permissive licenses are software licenses where the end user has many rights over what they can do with the software, including re-distribute it with their own license. This allows people to make proprietary software based on existing open source software:

A permissive software license, sometimes also called BSD-like or BSD-style license, is a free-software license which ... carries only minimal restrictions on how the software can be used, modified, and redistributed, usually including a warranty disclaimer. - Permissive Software License, Wikipedia

Examples of this type of license include the Apache 2.0 License, MIT License and BSD License.

3. Copyleft Licenses

Copyleft licenses are more restrictive licenses which ask the end user to further license their derivative works under a similar copyleft agreement (called reciprocity):

Instead of allowing a work to fall completely into the public domain, where no ownership of copyright is claimed, copyleft allows authors to impose restrictions on the use of their work. One of the main restrictions imposed by copyleft is that derived works must also be released under a compatible copyleft license. - Copyleft, Wikipedia

Copyleft licenses can present a problem for many organisations as they are fundamentally incompatible with either proprietary licenses or permissive licenses. An example of this type of license is the GNU Public License.

Proprietary Licenses

For proprietary software, source code is generally not made available to the end user. Where it is, there are usually strict non-disclosure agreements in place:

Proprietary software is software that is deemed within the free and open-source software community to be non-free because its creator ... exercises a legal monopoly by modern copyright and intellectual property law to exclude the recipient from freely sharing the software or modifying it ... thereby restricting their freedoms ... It is also known as non-free software or closed-source software - Proprietary Software, Wikipedia

Other Types Of License

Often there is an overlap between genuine open source licenses other models:

  • Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. Source code is often available but this is not a requirement.
  • Shareware - a type of proprietary software that is initially shared by the owner for trial use at little or no cost. Again, source not generally available.
  • Freemium - a portmanteau of the words "free" and "premium", is a pricing strategy by which a basic product or service is provided free of charge, but money (a premium) is charged for additional features, services, or virtual (online) or physical (offline) goods that expand the functionality of the free version of the software.

Unlicensed Software

Sometimes, the license is not provided on a piece of software, or, a license is named but no associated legal definition exists for it, or the software could be pirated either deliberately or accidentally by staff.

GenesisIT summarises the following risks around this:

  • Legal Risk - since the author of the software could litigate if they discover the infringement of their copyright.
  • Operational Risk - if the software doesn't work or introduces security issues.

Identifying The License

The license for an open source project is usually held in a file called LICENSE in the repository or library. (For example, FDC3's license is here:

Although this file allows for practically infinite variation in license terms and conditions, most open source software uses one of just a few common licenses.  For this reason, SPDX introduces license identifiers. For example, the SPDX identifier "Apache-2.0" refers to the Apache 2.0 License

Open Source Initiative (OSI) Open Source Definition

The Open Source Initiative (OSI) is an organisation keeping track of the different open source licenses in common use.

The previous section of this article gave an overview of what that meant and compared open source licenses to other types. However, OSI goes further than this and publishes an Open Source Definition explaining in simple terms what they regard open source to mean exactly. This includes:

  • Free Distribution
  • Source Code and license are available
  • Must allow "derived works", that is:
    • allowing code to be changed or patched
    • allowing building on top of the original work
  • No limits on:
    • who can use it
    • what it can be used with
    • which products it can be used in
    • the technologies it can be used with
    • the other software it can be used with

See: Open Source Definition

Open Source Initiative (OSI) Approved Licenses

Many of the most popular licenses are OSI Approved, that is:

Open source licenses are licenses that comply with the Open Source Definition – in brief, they allow software to be freely used, modified, and shared. To be approved by the Open Source Initiative (also known as the OSI) a license must go through the Open Source Initiative’s license review process. - OSI Approved Licenses, OSI

The OSI describes the definition of open source here: and describes how various common open source licenses differ here:

The vast majority of open source software will be using an OSI-approved licenses, but organisations will need to track their usage.

Changing Licenses

Sometimes, software can change license between versions and it is easy to be caught out not complying to the new license. Example: XCeed Property Grid changed license between 3.8.0 (MSPL License) and 4.0.0 (their own license). The newer license was non commercial only. Proper License Management Software is required to guard against this.

"Source Available" Licenses / Dual Licenses

A recent trend (2021) in software appears to be to move away from approved OSI licenses and towards Dual Licensing with a copyleft license and a commercial license. This occurred as a reaction to cloud providers such as AWS providing commercial products (and paid support) on their platforms, under-cutting the Freemium business models of the software developers.

In dual-licensing, a vendor releases software under a FOSS license with obligations that are difficult for some businesses to meet and also offers that same software under a commercial license. Both models use open source for exponential growth. The developer that grabs the free and open product today is (or works for) tomorrow’s paying customer. - What’s up with these new not-open source licenses? - Justin Colannino, Github

Popular examples include:


License Obligations

Within the three broad types of open source license described above, each license will differ by the permissions it gives, the limitations it reserves and the conditions on which it grants usage.  

GitHub provides a useful summary for most of the popular licenses when you view the LICENSE file in the repository.  For example:

GitHub's License Summary Card 1

GitHub's License Summary Card 2

Both of these licenses are open source, however the Apache License 2.0 is much more compatible with private/corporate software development as there is no condition that derived works are also open source. The important take-away here is that open source licenses can differ widely in what they require and legal counsel will need to be sought to define which are acceptable.

Note that different usage situations will also determine which licenses are acceptable.  For example, use behind the firewall may allow a wider selection of licenses than usage to customers over the public network.

Final Points

  • Not all open source software is licensed in the same way.
  • It is important to understand the licenses of the open source software you are using.
  • In particular, for commercial use, open source software with a copyleft license is problematic and needs to be carefully considered from a legal standpoint before use.

License Compliance Management

There are several key points that a large enterprise should consider to ensure compliance with open-source license obligations:

Further Reading

  1. CopyLeft article on Wikipedia.

  2. A guide to the GPL v3 explaining the philosophy behind the Copyleft GPL License.

  3. GitHub's ChooseALicense Site. A simple site that helps you navigate the choice of license for new software projects.

  4. Open Source Initiative's License Browser. Try choosing "Popular/Strong Community" for the most commonly used licenses.

5, Wikipedia's Softeware License Page contains two excellent tables summarising "Rights Granted" vs different types of software license.