The GNU General Public License ("GPL") is one of the most popular open source licenses. All software released by the Free Software Foundation and many other authors, are governed by this license. GPL provides the freedom to share and modify software under certain conditions.

Copy, Run and Distribute

GPL allows a person to copy, run and distribute the software governed by it. A person is allowed to distribute verbatim copies of the software, commercially or non-commercially, under the following conditions:

·         Source code is made available in any medium;

·         A copy of GPL accompanies the software;

·         A copyright Notice is affixed conspicuously on each copy and

·        The copyright notices relating to non-existence of a Warranty are kept intact

Modification

GPL allows a person receiving software under the license to modify the software. The modified software may be distributed under the following conditions in addition to the conditions mentioned above:

·        A notice relating to modification and date of modification accompanies the software;

·        A notice relating to applicability of GPL and any additional terms is provided with the software; and

·        The entire software along with the modifications is distributed.

Non-source transfers

The license allows a person to transfer software in the form of object code provided source code is made available in any of the following ways:

·        On a durable physical medium customarily used for software interchange, if object code forms part of a product;

·       By a written offer, valid for at least three years to make the source code available on a durable physical medium customarily used for software interchange, if the object code forms part of a product.

·         Through an equivalent access as that of the object code; and

·         At a specified location in case of peer to peer transfers of object code.

If an object code is transferred as part of a consumer product, installation information has to be made available along with the source code.

Additional Terms

As per the GPL, a person may supplement the terms of GPL with his own terms for material added by that person.  Only the following terms of the license may be supplemented:

·         Warranty and Liability;

·         Preservation of notices relating to author attribution or other notices;

·    Prohibition of modification of original notices or requiring modified versions to be marked differently;

·         Limitation of use of the author's name for publicity or prohibition of use of trademarks or trade names;

·         Indemnity of licensor or author in certain circumstances;

·       Any additional term outside the scope of the aforementioned terms is not allowed under the license.

Termination

Any violation of GPL will result in termination of the license. On receiving a notice of termination, if a violator rectifies his violation within 30 days from the date of receiving the notice, the license will not terminate. Termination of license of a person will not terminate the licenses of any one who had received the software from that person.

Patents

GPL considers patents to be inherently averse to freedom to develop software. A person who receives software under GPL is not allowed to assert any patent rights in such software against any person exercising rights under the license. If a person distributing software under GPL holds patents, he is deemed to have given a patent license along with such a transfer. If any person grants a patent license over software under GPL to a few persons, the patent license is deemed to extend to everyone, who receives the software from such persons.

No Warranty and Liability

Any software transferred under GPL comes without any warranty relating to it's fitness for a specific purpose. If the software fails to perform in an expected manner, it is the responsibility of the person implementing the software to repair or modify it to suit his needs.

As per GPL, a person who transfers software under GPL is not liable for any damages arising out of the use or inability to use the software.

Technology measures

A person is not allowed to restrict access to software governed by GPL by using technology measures. In case of existence of such measures, the person is not allowed to enforce any circumvention of such measures by any one receiving the software under GPL.

Business

The GPL provides opportunities to carry out business using the software governed by it in a number of ways. A company receiving software under GPL is allowed to modify and run the software for its own purposes. It is not required to make the source code for such modifications for internal use available to any one.

GPL also allows a person to carry out business by charging for physical transfer of software governed by it. The software may be transferred alone or in association with other software governed by the same or a different license. GPL also permits business via support or customization services relating to the software. Furthermore, GPL also permits a person to do business by providing warranty or liability provisions in the license as it comes with no warranty and limited liability under GPL.