It may be a little out of concept for this forum, but it’s related to Free Software as a whole idea.
Recently a big organization told me that they want to ditch Firebase and switch to Free Software alternatives. They asked me to do a research and bring up some different instances for replacing Firebase to test them and chose a couple of them to run primarily.
I wanted to ask you which services do you recommend to be used as a replacement, either as separate services or a complete package.
As pointed out, Firebase does a lot of things. Maybe you could specify which features they need?
FCM: UnifiedPush (has a client available at F-Droid, and would leave the user a choice for their preferred push notification provider – even FCM if they insist), other candidates
As it is, we do not know which features they use (or in your terms, which dependencies have been established). Second, some folks might know valid replacements but aren’t aware of the fact as they e.g. never used Firebase – so you’ll miss their hints if you don’t name required features explicitly. We really love to help, but we need to know how