The Difference Between Free Software and Open Source Licenses: A Practical Guide for Developers

Freedom Is Not Free of Charge

When we say “Free Software,” the word “Free” here means freedom, not zero cost. You can sell free software, just as you can offer software for free that is neither free nor open source. This fundamental distinction is what creates the confusion between the concepts of “Free Software” and “Open Source Software.”

The two concepts are close but not identical. Free Software focuses on the user’s freedom to run, study, modify, and redistribute the program. Open Source Software focuses on making the source code available under terms that allow use, modification, and redistribution, within standards defined by the Open Source Initiative (OSI).

The core difference between licenses like MIT, Apache, GNU GPL, and BSD is not whether they are open source, but what they allow you to do with the code, and what they require when you redistribute, modify, or embed it into another project.

Comparison of Major Software Licenses

License	Type	Allows Commercial Use?	Requires Publishing Your Modifications When Distributing?
MIT	Permissive	Yes	No
Apache 2.0	Permissive with patent provisions	Yes	No
BSD 2-Clause / 3-Clause	Permissive	Yes	No
GNU GPL v2/v3	Free with strong Copyleft	Yes	Yes, when distributing the derivative work under the license
GNU LGPL	Limited Copyleft for libraries	Yes	Depends on the nature of the modification and distribution method
GNU AGPL	Copyleft covering network use	Yes	May require making the source available to users interacting over the network
MPL 2.0	File-level Copyleft	Yes	Modifications to covered files remain under MPL when distributed

This is a practical summary, not a substitute for the license text. Precise obligations depend on how the code is integrated, the nature of the work distributed, and the version used.

What Is the Core Difference Between MIT, Apache, and GNU GPL?

MIT — Maximum Flexibility

It allows you to use, modify, and embed the code into a closed-source commercial project, and even sell a product built on it, provided you comply with the copyright notice and license text.

Example: You create a library under MIT and a company uses it inside a paid program that does not publish its source code. This is generally permitted under MIT. What to watch out for: MIT does not require the company to publish modifications to your library, nor does it include an explicit, detailed patent grant like Apache 2.0.

Apache 2.0 — Flexibility with Clearer Patent Protection

It is similar to MIT in allowing commercial use, redistribution, and embedding code into closed-source programs. However, it includes an explicit grant of certain patent rights from contributors, specific notice and change requirements, and a clause to terminate the patent license under certain conditions if specific lawsuits are filed.

Example: Developing a commercial application using an Apache 2.0 library without fully open-sourcing the application is possible, while respecting the license terms. When to choose it? When you want a flexible license for a project that may be used by companies or embedded in commercial products, with clearer handling of patent issues.

GNU GPL — Freedom to Reuse While Preserving Freedom

GPL differs from MIT and Apache in the principle of Copyleft: if you distribute a derivative program covered by GPL, you must respect GPL’s terms regarding licensing and source availability, and you cannot simply convert that derivative work into a closed-source program under proprietary terms.

Example: You modify a GPL program and distribute your executable version to clients; the requirements of the relevant GPL version apply to you, including source availability requirements in the required manner.

Important: GPL does not mean you are obligated to publish every private modification you keep for yourself, nor does it prevent selling the program or offering paid services related to it.

What Do Other GNU Licenses Mean?

GNU is not the name of a single license, but the name of a project and operating system, and it has several licenses that differ in scope:

License	Primary Purpose
GPL-2.0 / GPL-3.0	Preserving the freedom of derivative software when distributed
LGPL	Facilitating the use of free libraries from other programs, including some closed-source ones, under its terms
AGPL	Addressing programs used over a network, where there may be no traditional distribution
GFDL	A license for certain documentation and text materials, not the usual choice for application code

Therefore, when you find a project labeled “GNU,” check the full license name and version number. For example, GPL, LGPL, and AGPL are not synonyms.

When Is a License Truly Open Source?

Simply publishing the source code on GitHub or allowing people to view it is not enough. A license is considered open source according to the Open Source Initiative (OSI) definition if it meets its criteria, including the following principles:

Allowing redistribution of the program.
Making the source code available.
Allowing derivative works and modifications.
Not discriminating against persons, groups, or fields of use.
Not requiring that the program be part of a specific product or technology to benefit from the license.

The OSI officially approves licenses after review, so it is advisable to check the list of approved licenses. If the code is only available for reading, or the license prohibits commercial use, modification, or redistribution, the project may be Source Available without being open source in the approved sense.

When Is Software Considered Free?

According to the Free Software Foundation (FSF) definition, a license must grant the user four essential freedoms:

Freedom 0: Run — Run the program for any purpose, without arbitrary restrictions based on the type of user or nature of use.
Freedom 1: Study and Modify — Access the source code, study how the program works, and change it to suit your needs.
Freedom 2: Redistribute — Copy and distribute the program to others, for free or for a fee.
Freedom 3: Distribute Modified Versions — Modify the program and make your modified versions available to others so they can benefit.

In practice, MIT, Apache 2.0, GPL, LGPL, and AGPL are all considered free licenses according to the assessments of the relevant bodies, despite their differing terms. The concept of free software does not require the program to be free of charge, nor does it require every license to mandate publishing all modifications.

Which License Should You Choose for Your Project?

The choice depends on the freedom you want to grant others, and whether you want to require those who distribute a modified version to keep the source available.

Choose MIT if… You want the maximum ease of reuse, including embedding your project into closed-source commercial programs, while retaining copyright and license notices.

Choose Apache 2.0 if… You want nearly the same commercial flexibility, with explicit provisions regarding patents, notices, and changes.

Choose GNU GPL if… You want those who distribute derivative works covered by the license to preserve the freedom and source availability requirements, rather than simply allowing them to be converted into closed-source programs.

Choose GNU AGPL if… Your project is a server or network application, and you want to address the case of modified versions being provided to users over the network under the license terms.

Summary

MIT: Broad freedom of use and reuse, with few restrictions.
Apache 2.0: Broad flexibility with clearer patent handling.
GNU GPL: Freedom to use, modify, and distribute while preserving Copyleft terms when distributing covered works.
GNU AGPL: A Copyleft approach that also addresses certain network use cases.

There is no single best license for all cases. What matters most is choosing the license that accurately expresses the project’s philosophy, then including the correct LICENSE file and respecting the licenses of libraries and resources you rely on.