Licence Summary

Open Source/Free Software licenses come in three blends: heavy, medium, and light. Below is a summary of the most popular license in each category.


Word Count: 5235

The granddaddy of open source licenses. The GPL enforces the "four freedoms" of free software.

  • you agree that anti-circumvention laws do not apply. a direct jab at the DMCA
  • sub-licensing is not allowed
  • distributing verbatim copies is allowed
  • distributing modified copies is allowed as long as the new version is under the same license and has a note saying you modified it
  • a binary-only distribution is fine as long as a link is provided to get the source code as well, for no extra cost
  • optionally, the provision can be added to not allow the use of trademarked names
  • acceptance of the license is not required to run the software
  • each contributor grants you a patent license
  • GPL licensed code can be mixed with GPL Affero licensed code
  • no warranty/no liability

The "Affero" version of the GPLv3 has an extra provision to cover a web service. Meaning if you write some kick ass youtube clone, and someone sets up that has modifications, the source for that version must be made available even though its not being distributed as a software package. the act of putting the service on the net is a kind of publishing. A quote follows. "Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge"

Apache Licence 2.0

Word Count: 1420

Short, readable.

  • You get a copyright license
  • You get a patent license
  • You may reproduce the work with or without modifications
  • The project name/trademark still belongs to the owner
  • The usual no warranty/no liability
  • sub-licensing is allowed

MIT License

Word Count: 171

Ah the MIT License. Basically in the public domain, with a liability disclaimer. Its reads so beautifully I'll paste it here: "Permission is hereby granted, free of charge, to any person obtaining a copy of this software... to deal in the Software without restriction...". You could take the code, rename it, relicense it to proprietary software, and that would be fine with this license. The MIT version is still available from whoever made it available in the first place.

  • no warranty

The simplified BSD license and FreeBSD license are very similar to the MIT license.