The GNU Affero General Public License (AGPL) is a free software license. It is widely regarded as the strongest copyleft license you can get. Copyleft is a concept developed by Richard Stallman (the founder of the free software movement and the GNU Project) as a concept as part of the GNU General Public License (GPL). The original license for Emacs (The first part of GNU, a text editor that is extremely powerful, it literally comes with a news reader and tetris pre-installed and has it's own programming language) was called the “Emacs Commune,” which basically said all changes must go to Richard himself so he could integrate them into the main program. This got annoying after Emacs got popular outside of his department at MIT, however, so he invented Copyleft and the GNU GPL v1. Basically, it doesn't matter what you do when you change it, but as soon as you distribute your version (eg. post it online), that version is automatically licensed under the GNU GPL. Basically, regular free software insures user freedom for users, copyleft insures user freedom for users of both your program and all spin-offs. AGPL is basically GPL but every time software is being used on a network (like a server) and somebody abscesses that network, it is considered distribution. This was created to prevent the problem of Service as a Software Substitute (“Cloud Computing”), which Google is guilty of a lot (like Google Translate, which they have proved is capable of working offline). I recently saw on Reddit that Google has banned the AGPL from being used inside its company. They said AGPL was too “restrictive.” This was frightening. The first reason was something that Edward Snowden had said. The gist of it was power. Power imbalance. Now, this makes sense. If they [Google] retain copyright in the form of proprietary licenses, they don't feel restricted, but the users [citizens of the world] are restricted. Google feels restricted using copyleft licenses because they don't have the freedom to take away freedom. Everybody is equal, and that is unalienable. Google doesn't like that. Google would be forced to let people make offline versions of Translate if it was AGPL licensed. But the freedom of users is more important than the freedom of people in power to restrict the freedom of users. As Thomas Jefferson once put it:

In questions of power, let no more be heard of confidence in man, but bind him down from mischief by the chains of the constitution.