The General Public License

" The GPL grants the recipients of a computer program the following rights, or "freedoms":

• to run the program, for any purpose

• to study how the program works, and modify it

• to redistribute copies
• to improve the program, and release the improvements to the public

In contrast, the end-user licenses that come with proprietary software rarely grant the end-user any rights, other than the right to use the software, although it is debatable whether one requires a license for use per se. It may even attempt to restrict activities normally permitted by law, such as reverse engineering

The GPL seeks to ensure that the above freedoms are preserved in copies and in derivative works. It does this using a legal mechanism known as copyleft, which requires derivative works of GPL-licensed programs to also be licensed under the GPL

The GPL is the single most popular license for free and open source software. As of April 2004, the GPL accounted for nearly 75% of the 23,479 free-software projects listed on Freshmeat, and about 68% of the projects listed on SourceForge

Prominent free software programs licensed under the GPL include the Linux kernel, the GNU Compiler Collection, and Perl. "

Affero General Public License

AGPL summarised at the Wikipedia

The AGPL was designed to close a perceived application service provider "loophole" (the "ASP loophole") in the ordinary GPL, whereby using, but not distributing the software, as would be the case for SaaS or cloud-based systems, the copyleft provisions are not triggered. The additional provision requires that the complete source code be made available to any network user of the AGPL-licensed work, typically a Web application.

The Free Software Foundation has recommended that the GNU AGPLv3 be considered for any software that will commonly be run over a network. The Open Source Initiative approved the GNU AGPLv3 as an open source license in March 2008.