What do you think about using https://get.fabric.io/ in apps in general and especially for f-droid listed apps? Should we use it for app development or better try to prevent its usage?
Thanks for your opinions.
Rapha
This is proprietary software, apps using it cannot be included into F-Droid main repo.
Oops, I didn’t even notice that. I started contributing to GitHub - Piwigo/Piwigo-Android: Piwigo Native Android App and have seen, that fabric libs are used, so I decided to ask. I would also be interested in comments about other non-free dependencies in there, as I am also new to Android development it is hard for me to see all those suspicious things.
Chrashlytics I also identified as worth removing…
I am only willing to contribute to this app if it is fully free, so I am happy to get some help to see what needs to be cleaned up!
And another idea: in case a project wants to use non-free libraries like Crashlytics in its PlayStore variant and still have a parallel version without, can anyone give advices to configure gradle scripts to support both, while f-droid will build the free variant?
I did not have done this in the past, but searching for examples on GitLab is relatively easy. If you find out more about this, you’re invited to updated the F-Droid docs about this topic 
You want to look at Gradle build Flavours:
Ok thanks. We now have a dedicated flavors
googlePlay and floss in which we replace the calls to nonfree libs by stubs. Is this enough? Or are there any conventions for f-droid in such cases e.g. for the flavor names?
The flavour name is mentioned in the build recipe. Most apps use floss, foss or fdroid I guess.