Guide to Freeware and Open-Source Software Licensing

The Fundamental Distinction: Free as in Freedom vs. Free as in Price

When we talk about "free software," the word "free" is doing double duty in English in a way it doesn't in many other languages. The free software movement, led by the Free Software Foundation, draws a sharp line between two entirely different concepts that the same English word covers:

Gratis Free as in price — you pay nothing to obtain or use the software. This is what most people mean when they say a program is "free."
Libre Free as in freedom — you are granted the right to use, study, modify, and redistribute the software. This is what the Free Software Foundation means when it says software should be "free."

These two concepts frequently — but not always — go together. Adobe Acrobat Reader is a classic example of software that is free as in price but emphatically not free as in freedom. You can download and use it at no cost, but you cannot view its source code, modify it, or legally redistribute it. The GNU/Linux operating system, by contrast, is free in both senses: it costs nothing and you can read, modify, and share every line of code. Understanding which kind of "free" applies to any given piece of software is the starting point for understanding its license.

Freeware

Freeware is software distributed at no monetary cost, but it is not open source. The author retains full copyright and typically places significant restrictions on what users can do with the software beyond simply running it. Common freeware terms include:

Personal use only — commercial use requires a paid license
No modification of the binaries or resources
No redistribution without explicit permission from the author
The author may monetize future versions or add paid features at any time

Well-known examples of freeware include IrfanView (the image viewer), WinRAR (which never actually requires payment despite its perpetual trial notices), VNC Viewer, TeamViewer for personal use, and older versions of Skype. Freeware is practical and legitimate but should not be confused with open-source software — the source code is closed, your rights are narrow, and the software can be discontinued, changed, or made paid at the developer's discretion.

Shareware

Shareware is an older distribution model that flourished in the 1980s and 1990s. The idea was to encourage users to try software for free and then pay if they found it useful. Modern software-as-a-service (SaaS) freemium models are the direct descendants of shareware. Classic shareware comes in three flavors:

Time-limited trial — the full software works for a set period (30 days is typical), then requires purchase to continue.
Feature-limited free tier — a stripped-down version is available indefinitely, with advanced features locked behind a paywall.
Crippleware — an extreme form of feature-limited shareware where core functionality is intentionally disabled, making the free version nearly unusable without purchase.

Open-Source Licenses

Open-source software is software whose source code is made available under a license that grants users the right to use, study, modify, and distribute the software and its derivatives. The Open Source Initiative (OSI) maintains the formal definition and approves licenses that meet it. Within the open-source category, there is a spectrum from permissive licenses (which place almost no restrictions) to copyleft licenses (which require derivative works to carry the same license).

GNU General Public License (GPL)

The GPL is the flagship license of the free software movement, written by Richard Stallman and the Free Software Foundation. It is a strong copyleft license: any software that incorporates GPL code and is distributed must itself be distributed under the GPL with full source code. This viral property is intentional — it ensures that free software remains free. The GPL family includes several variants:

GPLv2 — the older version, used by the Linux kernel and thousands of other projects
GPLv3 — adds protections against tivoization (hardware that accepts only manufacturer-signed software) and software patents
LGPL (Lesser GPL) — a weaker copyleft version intended for libraries; programs that link to LGPL libraries are not required to be GPL themselves
AGPL (Affero GPL) — extends the GPL's copyleft to network-delivered software, closing the "application service provider loophole"

Full text and plain-language summaries of all GPL variants are available at gnu.org/licenses.

MIT License

The MIT License is one of the most permissive and widely used open-source licenses in existence. It grants users the right to use, copy, modify, merge, publish, distribute, sublicense, and sell copies of the software with almost no conditions. The only requirements are that the original copyright notice and license text be included in all copies or substantial portions of the software.

The MIT License is extremely popular among web developers and JavaScript library authors because it imposes no restrictions on commercial use and does not require derivative works to carry the same license. Commercial users — including large technology companies — heavily use MIT-licensed software in proprietary products without any obligation to release their own code. If you are writing a library and want maximum adoption, MIT (or Apache 2.0) is typically the right choice.

Apache License 2.0

The Apache License 2.0 is similar to MIT in permissiveness but adds an explicit patent grant — contributors to Apache-licensed software grant users a royalty-free license to any patents they hold that are infringed by the software. This makes it a safer choice for corporate environments where patent litigation is a concern. It also requires that any modifications be noted with a NOTICE file or changelog entry. Apache 2.0 is used by many major projects including Kubernetes, TensorFlow, and the Android operating system.

BSD Licenses

The BSD licenses originated at the University of California, Berkeley, and are another family of permissive licenses. Like MIT, they allow almost unrestricted use, modification, and redistribution. There are three main variants in active use:

2-Clause BSD ("Simplified BSD") — requires preservation of the copyright notice and disclaimer in source and binary forms. Nearly identical to MIT.
3-Clause BSD ("New BSD") — adds a non-endorsement clause: you may not use the names of the original project or its contributors to endorse derivative works without permission.
0-Clause BSD (BSD Zero Clause) — essentially public domain; no conditions whatsoever. Suitable when you want maximum freedom with no attribution requirement.

Mozilla Public License 2.0 (MPL)

The Mozilla Public License 2.0 occupies a middle ground between permissive licenses like MIT and strong copyleft licenses like GPL. Its copyleft is file-level rather than project-level: if you modify an MPL-licensed file, you must release that file under the MPL. But you can combine MPL files with proprietary code in a larger work without triggering copyleft on the proprietary portions. This makes it popular for projects that want to protect their own code while allowing integration into commercial products. Firefox, Thunderbird, and LibreOffice's core components are MPL-licensed.

Creative Commons Licenses

Creative Commons licenses are designed primarily for creative works — art, music, writing, photography, and documentation — rather than software, though they appear in software contexts for assets, documentation, and datasets. The main variants are:

CC BY (Attribution) — use freely, in any way, but credit the creator. The most permissive CC license that requires attribution.
CC BY-SA (Attribution-ShareAlike) — use freely, credit the creator, and license derivatives under the same terms. The Creative Commons equivalent of the GPL.
CC BY-NC (Attribution-NonCommercial) — use freely for non-commercial purposes only, with attribution. Not considered an open-source license by the OSI.
CC0 (No Rights Reserved) — the creator waives all copyright to the extent possible. Effectively public domain worldwide. Suitable for data, scientific research outputs, and government works.

The full range of Creative Commons licenses, with human-readable summaries and legal code, is available at creativecommons.org.

License	Commercial Use	Modify	Distribute	Share-Alike	Patent Grant
MIT	✓	✓	✓	—	—
Apache 2.0	✓	✓	✓	—	✓
BSD (2/3-Clause)	✓	✓	✓	—	—
MPL 2.0	✓	✓	✓	File-level	✓
LGPL v2/v3	✓	✓	✓	Library only	—
GPL v2/v3	✓	✓	✓	Yes (copyleft)	—
AGPL v3	✓	✓	✓	Yes + network	—
Freeware	Often limited	✗	✗	—	—

Proprietary Licenses

Proprietary software licenses (sometimes called End User License Agreements, or EULAs) grant the user a limited right to use the software while the vendor retains all other rights. Typical restrictions in proprietary licenses include:

Prohibition on reverse engineering, decompiling, or disassembling the software
Prohibition on redistributing, reselling, renting, or lending the software
Strict limitation of liability — the vendor disclaims all warranties to the maximum extent permitted by law
The license may be revoked if terms are violated, at which point you lose the right to use the software even if you paid for it

Choosing Software by License Type

The right license to look for depends on how you intend to use the software:

Building a commercial product — Prefer MIT, Apache 2.0, or BSD. Avoid GPL unless you are prepared to open-source your entire codebase. LGPL is acceptable if you are only linking to the library and not incorporating its code.
Running a cloud or SaaS service — Be aware of the AGPL: if you use AGPL software in a network service, you must release your source code to users of that service. MIT and Apache 2.0 carry no such obligation.
Academic or research use — Almost any license is fine for private research. For published tools and datasets, CC0 or MIT signals openness and encourages citation.
Personal or hobbyist use — License constraints rarely matter for personal use. Even the GPL allows you to modify and run software privately without sharing the changes.

A Guide to Freeware and Open-Source Licensing