AGPL
The GNU Affero General Public License (AGPL) is a strong copyleft license in the vein of the GPL, but focusing on server based applications.

Of particular interest is section 13

13. Remote Network Interaction; Use with the GNU General Public License.
Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software. This Corresponding Source shall include the Corresponding Source for any work covered by version 3 of the GNU General Public License that is incorporated pursuant to the following paragraph.

Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the work with which it is combined will remain governed by version 3 of the GNU General Public License.

which attempts to guarantee the four freedoms to users of a network application.

This has implications for the licensing of projects with AGPL components, especially in languages like Common Lisp where there isn't always a clear distinction between calling an external library and creating a derivative work of that library.


License