je confirme après une légère recherche que GeoGebra n'est pas libre :
"You are free to copy, distribute and transmit GeoGebra for non-commercial purposes (please see details below)."
donc pas de 4e liberté.
C'est un peu plus compliqué quand on regarde :
Is GeoGebra free and open source software?
GeoGebra is open source software and available free of charge for non-commercial users. You can find our source code online and we are actively collaborating with the open source community and other open source projects used by GeoGebra. Thanks a lot to all contributors of these projects for their great work!
Please note that GeoGebra as a complete software program would probably not be considered "free" software according to the definition of that term which is used by the Free Software Foundation. This is because the restrictions on commercial use that apply to the GeoGebra installers, web services and language files add-ons might be seen to be a restriction on the software as a whole (thus making it "non-free"), even though the GeoGebra source code is made available under the GNU General Public License without restriction. You can rest assured that our license terms fully respect all existing licenses from third parties (including the GNU General Public License and all Creative Commons variants) and have been checked by an experienced law firm.
en tout cas, une chose est sûre : ils ont l'air sûrs d'eux ;) et tout paraît explicite.