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This page describes the fundamental attributes of different Free Open Source Software licenses from a legal perspective.


The nature of Free Open Source Software licenses can be understood by considering the two extremes of the field, the generally believed to be maximally restrictive GPL License and the near public domain BSD License, which differ mainly in their treatment of source code compared with binary code.

    Source code is human readable, containing statements like:
              if (circle = selected ) draw 1;
    To run on a computer, source code is translated to binary code, 
    losing structure and is not human modifiable, producing code like:

The key innovation of the GPL license was the requirement that source code be provided along with any binary code produced from the source, ensuring that recipients have the freedom to modify the source themselves for any purpose they wished. This feedback loop was intended to be an innovation engine for a field believed to hold more in common with mathematics than industrial development, and where the possibilities for humanity were nearly endless and the benefit of many hands great.

In contrast, consider the nearly public domain BSD License. In the Free Open Source Software tradition, BSD also requires modifications, additions, enhancements, and other changes to source to be licensed under BSD, but freedom with any binaries produced is absolute, with no requirements to make the source available at all. For this reason BSD is sometimes said to be more business friendly, because it allows inclusion of BSD binaries in commercial products without restrictions. Now, should modified BSD source be made available to others, whether purposely submitted to the community or published by mistake, it is pure Free Open Source Software and so free to anyone who receives it to use, modify, and distribute. The key difference is that legally release of BSD source is completely at the discretion of the holders.

In practice, the range of Free Open Source Software licenses from GPL to BSD have all shown that freedom to access and fork the code usually leads to the opposite, an improving code base and growing ecosystem where each participant receives more than they contribute.

Certification Body

The authority for designating licenses that comply with the essential freedoms required by Free Open Source Software is the Open Source Initiative.

License Matrix

A comparison of some Free Open Source Software licenses across common attributes is shown in the table below. Note all Free Open Source Software licenses satisfy the first four attributes.

  Source must be free Must retain copyright notice Can sell executable without restriction Modifications covered under license Prevented from use for software or data locking Linked code covered under license New updates to license will apply Patent retaliation, loss of use if suit brought Can sell source code
GPL V3 Y Y Y Y Y N Y  ? N
Mozilla (V1.1) Y Y Y Y N N Y Y N

Free Open Source Software Licenses

Free Open Source Software licenses include: