Geogebra

https://www.geogebra.org/license

The functional core is under the GNU GPL, hence free software. It even is available in Trisquel's repository. For that same reason, the installer being proprietary does not matter to you because you will not use it. The so-called "language files" cannot be used in a commercial way, hence violating freedom 0. Most of us would consider that OK when it comes to non-functional data. However "translation files" and "documentation" are functional data. They serve to use the software, to achieve a goal. The "resources" (including graphics) probably aim to learn geometry. If so, they are functional and commercial usages should be allowed as well. I do not know what the web services are for. They probably SaaSS: https://www.gnu.org/philosophy/who-does-that-server-really-serve.html

If I were you, I would try to install the "geogebra-gnome" (or "geogebra-kde") package from Trisquel's repository and see if it is any useful by itself, i.e., without downloading any additional file or accessing any Web service.

I can confirm it is in the Debian main repo.

Ok thanks, I think I'll install the one that is in the Trisquel's repo to be sure that is free.