3D software like GeoGebra Does it exist a free interactive geometry software, like GeoGebra, which works for 3D geometry? I would be able to draw spheres, great circles, and so on.
GeoGebra 5.0 (with 3D) has been released:

https://www.geogebra.org/
If you're on a mac, theres a plotting software build in.
Go to Applications / Utilities / Grapher.
It's easy and powerful, can plot 2D and 3D graphs.