Fairphone Open OS promotes F-Droid
"The Fairphone Open Source OS includes the standard Android operating
system (version 5.1) plus all the special Fairphone features. Google
Mobile Services (GMS) are NOT included, so you will need to find
alternatives for things like email, maps, a browser and more. Once you
start looking, you’ll be surprised by how many options are available,
such as F-Droid, an alternative app store. Also, in this version, root
access can be easily enabled via the developer settings."