OpenBoard
Interactive whiteboard for schools and universities.
It’s free
https://openboard.ch/index.en.html
Geogebra
Geogebra Classic joins graphing, geometry, 3D, spreadsheets, computer algebra and probability in one easy-to-use and powerful package. Millions of people around the world use GeoGebra to learn math and science.
It’s free
https://www.geogebra.org/classic?lang=en