The STACK source code is Licensed under the GNU General Public, License Version 3.
The STACK documentation, contained in the source code subdirectories of
doc/, is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
STACK imposes no requirements on users to choose a license for learning materials they write from scratch. We are aware of open (e.g. Creative Commons), closed, and commercial uses of STACK materials. Users remain responsible for respecting existing licences attached to shared learning materials.
It is possible to embed other media inside STACK questions. Users of STACK remain entirely responsible for complying with licenes for materials and media embedded inside STACK questions. Please note that the GeoGebra's license does not match the STACK licence.