Collaboration was the basis of our Erasmus+KA2/ etwinning project in all its tasks. Geogebra files, Geogebra books, Geogebra teaching and learning and a lot of MATHS activities!!!
Many working results can be found here:
https://www.geogebra.org/m.a.t.h.s.
For example
Look here and play:
http://www.geogebra.org/m/YvqbpGws#material/PcfNh4t