Android development. Are there services for free synchronization of user data?

Question

Android

There was a task to provide users with the ability to synchronize data between devices.
Cloud storages like Azure, Amazon, Google are all paid. Is there a free alternative?
This is not about file sharing, but about data from the database, respectively, I would like to have something like a noSQL database on that side.

Answer 1

Firebase is free to use until limits are reached.

Answer 2

Won't go. Firebase is more for centralized distribution of messages to different clients.
And here each client has its own repository, and accordingly, each client needs enough space (at least 1Gb).
Well and plus any system of "registration" transparent for the client is necessary, using API of this DBaaS (if I correctly understand terminology).
Something similar seemed to me in OpenDrive , in any case, there is an API for "seamless registration" there. But there are other limitations that I don't know. how to bypass. This is not DBaaS, and of course, it is problematic to build synchronization there - you can’t download horse-sized amounts of information every time.