⚖️ Open Source Licenses Explained

Author

Liam Gill
January 23, 2025

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Open Source Basics and Key License Categories

Open source software (OSS) is the backbone of modern technology, powering everything from web frameworks to entire operating systems. It thrives on the principles of transparency, collaboration, and community-driven innovation. However, at its core lies a critical consideration: licensing. Open source licenses define how software can be used, modified, and distributed, ensuring legal clarity for both creators and users.

Open source licenses can be broadly categorized into two types: permissive and copyleft.

  1. Permissive licenses (e.g., MIT, Apache 2.0) offer minimal restrictions, allowing almost unrestricted use of the software, including incorporation into proprietary projects. These are popular with businesses due to their flexibility.

  2. Copyleft licenses (e.g., GPL, AGPL) promote freedom by requiring that any modifications or derived works also be licensed under the same terms, ensuring the software remains open source.

Beyond these, there are licenses that blur the lines—“faux-pen” source models or ethical licenses, which restrict certain uses or include commercial clauses. Public domain dedications, such as CC0, take openness a step further by waiving all rights, though their legal enforceability can vary by jurisdiction.

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Permissive Licenses – Freedom with Flexibility

Permissive licenses are often seen as the “easy-going” option for open source software. They grant users broad rights to use, modify, and distribute code with minimal obligations. Here’s a breakdown of key permissive licenses:

  1. MIT License:

    • Simplicity reigns supreme with this 200-word license. Users need only include the original license and copyright notice.

    • It’s popular for projects like React and Ruby but lacks explicit patent protection, which can be a concern for software involving patented technologies.

  2. Apache License 2.0:

    • Provides an explicit patent grant, shielding users from litigation over patented contributions.

    • Heavily used in projects like the Android Open Source Project, it balances clarity with legal robustness, albeit at the cost of greater complexity.

  3. BSD Licenses (2-Clause and 3-Clause):

    • Similar to MIT but with nuanced differences like a “no endorsement” clause in the 3-Clause variant.

These licenses empower businesses to innovate freely while ensuring the original creators receive proper attribution.

Copyleft Licenses – Preserving Openness

Copyleft licenses prioritize keeping software open source. By requiring derivative works to remain under the same license, they protect the community-driven ethos of OSS.

  1. GNU General Public License (GPL):

    • GPL v2.0: Foundational copyleft license, requiring derivatives to stay open source. Used by Linux, a cornerstone of modern infrastructure.

    • GPL v3.0: Updates include patent protection and anti-DRM provisions but faced resistance over stricter terms.

  2. GNU Affero General Public License (AGPL):

    • Addresses the “SaaS loophole” by requiring source code release for web services running modified OSS. Ideal for cloud-based projects.

  3. GNU Lesser General Public License (LGPL):

    • A “weaker” copyleft license, allowing proprietary software to link to open source libraries while maintaining copyleft provisions for library modifications.

Copyleft ensures contributions to OSS remain open and available, making it ideal for community-driven projects but sometimes challenging for proprietary business models.

With a clear understanding of open source license types, you’re better equipped to choose the right one for your project’s goals—whether fostering open collaboration, enabling commercial use, or balancing the two.

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