Open-source software forms the backbone of countless applications, from the smallest utilities to the infrastructure running the largest data centers. The licenses under which this software is released can significantly affect how it’s used, integrated, and distributed. This blog post aims to demystify open-source licenses, highlighting their key characteristics, especially in terms of legal compliance and commercial compatibility.
1. MIT License
Description: One of the most permissive and straightforward open-source licenses. It allows almost unrestricted freedom to use, modify, and distribute the licensed software, provided that the original license and copyright notice are included with any substantial portions of the software.
Commercial Compatibility: Highly compatible. Its permissiveness makes it favorable for commercial use, without imposing significant legal constraints on distribution.
2. Apache License 2.0
Description: Similar to the MIT License in its permissiveness, the Apache License also provides an express grant of patent rights from contributors to users. It allows for commercial use, modification, and distribution of the licensed software.
Commercial Compatibility: Generally considered commercially friendly. It requires explicit attribution and provides an explicit grant of patent rights, reducing legal risks for commercial applications.
3. GNU General Public License (GPL) Versions 2 & 3
Description: The GPL licenses are copyleft licenses, which means that any derivative work must be distributed under the same license terms. Version 3 (GPLv3) introduced terms intended to protect against patent aggression and to prevent tivoization (the practice of designing hardware to prevent modifications to the software it runs).
Commercial Compatibility: GPLv3 is often considered commercially “toxic” because it requires that derivative works be open-sourced under the same license, potentially exposing proprietary code. GPLv2 is seen as slightly more lenient, though still challenging for commercial proprietary use.
4. GNU Lesser General Public License (LGPL)
Description: A compromise between the strong copyleft of the GPL and permissive licenses like MIT and Apache. It allows linking to open-source libraries (under LGPL) in proprietary software without the requirement to release the proprietary software’s source code.
Commercial Compatibility: More commercially friendly than GPL, especially for use in proprietary software that uses open-source libraries without modifying them.
5. BSD Licenses (2-clause and 3-clause)
Description: The BSD licenses are permissive, similar to the MIT License. The 2-clause license is very straightforward, allowing for almost unrestricted use, while the 3-clause license adds a non-endorsement clause, preventing the use of the licensor’s name to promote derived products without permission.
Commercial Compatibility: Both are considered commercially friendly due to their permissiveness and minimal requirements.
6. Mozilla Public License 2.0 (MPL 2.0)
Description: A middle-ground license that allows the code to be combined with proprietary software. It requires that modifications to the licensed code be open-sourced, but allows for the combination of the MPL-licensed code with proprietary code into a larger work without open-sourcing the proprietary components.
Commercial Compatibility: MPL 2.0 is seen as commercially friendly, especially for projects that want to ensure improvements to open-source code are shared while allowing for commercial application development.
7. Eclipse Public License (EPL)
Description: Similar to the MPL, the EPL is a moderate copyleft license that requires that modifications to EPL-licensed code be made available under the EPL, but allows for proprietary applications to link to EPL-licensed libraries without open-sourcing the proprietary code.
Commercial Compatibility: The EPL is generally considered to be commercially friendly, especially for developers looking to use open-source libraries within proprietary applications without distributing the entire source code.
8. Creative Commons Licenses
Description: Creative Commons licenses are not typically used for software but for creative works such as videos, photographs, and documentation. CC licenses come in various forms, from the most permissive (CC0, which is essentially public domain) to more restrictive forms (such as CC BY-NC-ND, which allows sharing but not commercial use or derivative works without permission).
Commercial Compatibility: The commercial friendliness of CC licenses varies. CC0 is highly compatible with commercial use, imposing no restrictions. Other, more restrictive licenses (like CC BY-NC-ND) limit commercial use and derivative works, making them less suitable for commercial projects that require modification or commercial distribution of the content.
9. GNU Affero General Public License (AGPLv3)
Description: Similar to GPLv3, but with an additional requirement that if you run a modified program on a server and let other users communicate with it there, you must also release the modified source code to those users. This license aims to close the “application service provider” loophole in the GPLv3.
Commercial Compatibility: Like GPLv3, AGPLv3 is considered challenging for commercial use, especially for software offered as a service, due to its requirement to share source code modifications.
10. European Union Public License (EUPL)
Description: The EUPL is a strong copyleft license approved by the European Commission. It is compatible with several other licenses, including the GPL, allowing for the integration of EUPL-licensed code with code under those licenses.
Commercial Compatibility: The EUPL’s copyleft nature makes it less commercially friendly for proprietary software, similar to the GPL. However, its compatibility with other licenses offers some flexibility for open-source projects.
11. Zlib/libpng License
Description: This is a very permissive license for software libraries that allows for modification, distribution, and use in proprietary applications, provided that credit is given to the author.
Commercial Compatibility: Highly compatible with commercial projects due to its minimal restrictions, making it favorable for use in both open-source and proprietary software.
12. Artistic License 2.0
Description: Originally designed for the Perl programming language, this license encourages artistic freedom by allowing modified versions of the software to be distributed under a different license or as closed source, provided that certain conditions are met.
Commercial Compatibility: This license is generally considered commercially friendly, offering flexibility for developers to use and contribute to open-source projects while retaining the option to distribute proprietary versions.
13. Redis License
Description: Redis uses a combination of open-source and proprietary licensing for different components of its software. The core of Redis is licensed under the BSD license, making it highly permissive and commercially friendly. However, certain Redis modules are licensed under the Redis Source Available License (RSAL), which restricts the use of the software in a database, caching, or a database-like functionality in a commercial product without purchasing a commercial license.
Commercial Compatibility: The core BSD-licensed part of Redis is commercially friendly. The RSAL for certain modules introduces restrictions intended to protect the commercial interests of Redis Labs, the company behind Redis, making those modules less suitable for commercial products seeking to use advanced features of Redis without engaging in a commercial relationship with Redis Labs.
14. MySQL License
Description: MySQL, one of the world’s most popular open-source relational database management systems, is dual-licensed. For open-source projects, it can be used under the GNU General Public License (GPL), which allows for free use, modification, and distribution under the same GPL license. For organizations wishing to incorporate MySQL into proprietary products, commercial licenses are available from Oracle Corporation, which acquired MySQL as part of its purchase of Sun Microsystems.
Commercial Compatibility: The GPL license for MySQL is suitable for open-source projects but can be restrictive for proprietary commercial use due to its copyleft requirements. The commercial licensing option provides the necessary legal framework for proprietary use but at the cost of licensing fees, making it a significant consideration for companies planning to use MySQL in their products or services.
Conclusion
The landscape of open-source and creative licenses is broad and varied, catering to different needs, goals, and legal requirements. Creative Commons licenses expand the scope of open-source principles to creative works, offering a range of options from completely unrestricted use to more controlled scenarios. Understanding the specific terms and implications of each license type is crucial for ensuring legal compliance and aligning with project or organizational goals, whether the focus is on software, documentation, or other creative content. Careful consideration and, when necessary, legal consultation can help navigate this complex landscape effectively.
This is not legal advice. Please consult a legal professional before making commercial decisions around licensing.
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