I read about this in the ct magazine and want to use it.
The setup would be 2 android devices, Windows and ubuntu linux.
How does the license work?
I will use FDroid and do I need 2 or just one license for the android devices?
Hey and welcome to the Cryptomator Community 
,
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regarding this topic.
On the desktop the same applies, if you want to support us, you can buy a supporter certificate for the desktop app which also can be used on any number of desktop devices you own.