If you're working with open-source software, you've probably come across terms like FOSS, GPL, MIT, or Apache License. But what do these licenses actually mean? How do they affect how you can use, modify, and distribute software?
In this blog, we'll break down what a FOSS license is, explore the most common types, and help you choose the right one for your project.
What is a FOSS License?
FOSS stands for Free and Open Source Software. A FOSS license is a legal framework that allows users to:
Use the software for any purpose
Study how the software works
Modify the software
Distribute copies of the original or modified software
These freedoms are designed to promote transparency, collaboration, and innovation.
But "free" doesn't always mean "without restrictions." Different licenses impose different rules around what you must do when you share or modify the software.
Categories of FOSS Licenses
FOSS licenses generally fall into two main categories:
1.Permissive Licenses
These licenses have minimal requirements. You can use, modify, and redistribute the software with few obligations. You don't have to use the same license in your derivative work. They're ideal for maximum flexibility and are often business-friendly.
Popular permissive licenses include:
MIT License
Apache License 2.0
BSD Licenses
2.Copyleft Licenses
These licenses ensure that derivative works are also distributed under the same license. If you modify and distribute the software, you must release the source code under the same terms.
Popular copyleft licenses include:
GNU General Public License (GPL)
GNU Lesser General Public License (LGPL)
Affero General Public License (AGPL)
Comparison of Common FOSS Licenses
LicenseTypeKey RequirementUsable in Proprietary Software?MITPermissiveMust include the original licenseYesApache 2.0PermissiveInclude notice and do not use trademarksYesBSDPermissiveInclude copyright and disclaimerYesGPLCopyleftMust open source derivatives under same licenseNoLGPLCopyleftLess strict; allows dynamic linkingYes (with conditions)AGPLCopyleftMust release source even if software runs as a serviceNo
Example: MIT License in Your Code
Here's how you might include an MIT license header in a Python script:
Which FOSS License Should You Choose?
Here are some general guidelines:
Use MIT or Apache 2.0 if you want your code to be widely reused, including in proprietary projects.
Use GPL if you want all derivative works to remain open source.
Use LGPL for libraries you want used in both open and proprietary software.
Use AGPL if you're building server software and want to ensure all modifications are shared, even when run as a service.
Conclusion
FOSS licenses are more than just legal jargon-they shape how software is shared, improved, and commercialized. Whether you're an open-source maintainer, contributor, or user, understanding these licenses empowers you to make informed, ethical, and strategic decisions.
Got a favorite FOSS license? Or a horror story about choosing the wrong one? Share your experience in the comments!
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