Licenses

Below, we have provided brief descriptions of the more commonly used open-source licenses. All of these open-source licenses share three central provisions:

The Apache license

The Apache license stipulates that any redistribution of the software include the text, "This product includes software developed by the Apache Software Foundation (http://www.apache.org/)." This is often called the "Acknowledgment Clause." The original BSD license had a similar clause as well, but it was removed in July of 1999. Having the clause promotes awareness of the product; removing it simplifies the act of redistribution. The Apache license also reworks the BSD's third restriction into a pair of restrictions that protect the name "Apache" from being used as the name of a derived product or to endorse the derived product.

The BSD license

Developed by the University of California, Berkeley, the BSD license is the most unrestricted of the open-source licenses. It allows for use, modification, and redistribution subject to three simple restrictions (paraphrased):

  • The files must retain their original copyright and license
  • Binary redistributions must include a copy of the copyright and license somewhere in the distribution
  • The names of the project creators and contributors may not be used to endorse products derived from the software without permission

It also includes a standard disclaimer of warranty.

The GNU General Public License (GPL)

The GNU GPL, created by the Free Software Foundation, was the first open-source license and, in its insistence on keeping source code free, it remains the strictest. In a nutshell, the GPL stipulates not only that all "free" code must remain "free," but that all code derived in part or in whole from such code must be fall under the same license terms as the original code. On the face of it, the license would seem to encourage nonprofit development and discourage commercial interests. However, as Brian Behlendorf has argued, the GPL can provide a vehicle for the widespread establishment of a platforms that indirectly enhance commercial interests.