The GNU GPL allows people to modify the software they receive, and share those modified versions with others, as long as they make source available to the recipients when they do so. However, a user can modify the software and run the modified version on a network server without releasing it. Since use of the server does not imply that people can download a copy of the program, this means the modifications may never be released. Many programmers choose to use the GNU GPL to cultivate community development; if many of the modifications developed by the programs users are never released, this can be discouraging for them. The GNU AGPL addresses their concerns. The FSF recommends that people consider using the GNU AGPL for any software which will commonly be run over a network.
Both GPLv3 and the GNU AGPL allow developers working on a project under one license to combine it with code released under the other. As a result, programmers who want to use the GNU AGPL for their own work can take advantage of the many libraries and other source files available under GPLv3. Developers working on GPLv3-covered projects will often be able to use modules under the GNU AGPL with minimal hassle as well, since the GNU AGPL's additional term has no requirements for software that doesn't interact with users over a network.
FSF board member Benjamin Mako Hill said, "The GNU GPL has been the most successful free software license because it makes a program's source available to its users. This enables massive collaboration between developers, since everyone gets the same benefits from this rule. The GNU AGPL will enable the same kind of cooperation around web services and other networked software."
A first draft of the GNU AGPL was published on June 5, and a second draft on August 14. The FSF heard comments on both through its web-based feedback system. "The GNU AGPL is very much a community license," said Peter Brown, Executive Director of the FSF. "The feedback we received while working on GPLv3 demonstrated a clear desire for this sort of license. And thanks to the community's help during the drafting, we're happy that the GNU AGPL meets those needs."
The final license is published here.