The Gnu Not UNIX group created the General Public License for a popular version of the UNIX operating system. They drafted the GPL to license this operating system software. Large mainframe computers were initially the only ones to use the system software. They originally published the GPL to enable distribution to other software developers. It was a framework for other open source licensing agreements. All open source agreements have the same stated altruistic goals of establishing freedoms for both the developers and the users of software. The GPL agreement attaches a preamble to it that declares these freedoms.
Gnu Not UNIX - www.gnu.org

The GPL was significant as the legal copyright instrument that was the core of open source software. This contractual agreement allows for more collaboration in the development of their GNU UNIX operating system. This system eventually made a metamorphosis into the Linux operating system. This GPL copyright document, or as the GNU liked to call it, the 'copyleft' document, founded all the freedoms that are inherent in the current open source software movement. The GPL licensing agreement is the basis for the Open Source Initiative's definition of an open source agreement.
Open Source Initiative - www.osi.org

The GPL has set a legal precedence for the software industry in the contracts between the entity that owns the software and the software user. This is new legal ground and the courts have not thoroughly tested these agreements. Since the intent is to provide the users with more freedom, there is not much reason for users to make litigious challenges. The intent of these agreements would seem to be clear and reasonable. Developers, on the other hand, have a deep interest in the how the terms of the open source contractual agreement are assessed by the litigators. Possible legal issues that developers might challenge involve software bundling, exemptions for program patches and the extent of the agreement. The courts will determine some of these issues.
Open Source Software Institute - www.ossi-news.org/mt