Brief Guide to Open Source Licenses in 2023

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Open source licenses allow developers to share their code with the public while also dictating how that code can be used, modified, and distributed. Different licenses cater to various philosophies and use cases. Here’s a comparison of some popular open source licenses:

  1. MIT License (MIT)
    • Advantages:
      • Very permissive: allows reuse in any project, including proprietary ones.
      • Simple and easy to understand.
    • Disadvantages:
      • Doesn’t ensure that derivative works are open sourced.
    • Popularity and Usage: One of the most popular licenses, especially for small projects and libraries. Examples: jQuery, .NET Core.
  2. GNU General Public License (GPL)
    • Advantages:
      • Ensures that derivative works remain open source (strong copyleft).
      • Protects the freedoms of end users.
    • Disadvantages:
      • Can be seen as restrictive, especially for commercial software.
      • Version incompatibilities (e.g., GPLv2 vs GPLv3).
    • Popularity and Usage: Used by many significant projects. Examples: Linux kernel (GPLv2), WordPress, and GNU tools.
  3. GNU Lesser General Public License (LGPL)
    • Advantages:
      • Similar to GPL but more permissive for libraries. Libraries under LGPL can be used in proprietary software.
    • Disadvantages:
      • Still requires derivative works or modifications to the library itself to be open sourced.
    • Popularity and Usage: Suitable for libraries that want to be more friendly to commercial software. Examples: GTK.
  4. Apache License 2.0
    • Advantages:
      • Permissive like MIT.
      • Express grant of patent rights from contributors to users.
      • Requires a change log for modifications, ensuring downstream users can track alterations.
    • Disadvantages:
      • Slightly more complicated than MIT.
    • Popularity and Usage: Used by many Apache Software Foundation projects and others. Examples: Apache HTTPD, Apache Kafka.
  5. BSD Licenses (e.g., 2-clause, 3-clause)
    • Advantages:
      • Very permissive.
      • Simple and concise.
    • Disadvantages:
      • The “BSD advertising clause” in the original BSD license led to complications (and eventually was removed in the 2-clause and 3-clause versions).
    • Popularity and Usage: The FreeBSD, NetBSD, and OpenBSD operating systems use variations of the BSD license.
  6. Mozilla Public License 2.0 (MPL 2.0)
    • Advantages:
      • File-level copyleft: Individual files that are modified must remain under MPL, but new files or works that only link to MPL-covered software do not.
    • Disadvantages:
      • More intricate than MIT or BSD licenses.
    • Popularity and Usage: Used by Mozilla projects like Firefox.
  7. Creative Commons Licenses
    • Advantages:
      • Flexible suite of licenses catering to various needs, from very permissive to more restrictive.
      • Not just for software, but for any kind of creative work.
    • Disadvantages:
      • Not intended for software, leading to potential ambiguities in that context.
    • Popularity and Usage: Widely used for artwork, music, blogs, and educational materials.
  8. Eclipse Public License (EPL)
    • Advantages:
      • Allows derivatives and distributions of modified works under other licenses.
    • Disadvantages:
      • Not as well-known as other licenses.
    • Popularity and Usage: Used by Eclipse IDE and other Eclipse Foundation projects.

Conclusion: Choosing a license depends on the developer’s goals. If they want maximum freedom and adaptability, MIT or BSD are excellent choices. If ensuring that derivative works remain open source is crucial, GPL might be the way to go. For something in between, MPL or LGPL could be ideal. As always, when considering licensing, it might be wise to consult with someone knowledgeable about intellectual property laws.