Share and Share Alike: Understanding and Enforcing Open Source and Free Software Licenses

On September 27, 1983, Richard M. Stallman began a software revolution with a post to the Usenet newsgroup, net.unix-wizards. He announced his plan to write a complete software system called GNU that would be compatible with the UNIX computer operating systems in wide use at the time. At the time, Stallman could not have known that the engine of his revolution was not going to be the free software that he and others would write, but a free software license that he would develop to implement his vision, the GNU General Public License (GPL). This paper describes the history and the commonly used software licensing in terms of the free software and open source movements. Next, the paper explains the GPL and the recent attempts to enforce the GPL. The GPL is a revolutionary copyright license that has allowed software developers to use existing law to copyright their work, while allowing licensees the freedoms to use, copy, modify, and distribute their work, but not to turn the work into a proprietary derivative.