In my app I have SQLite db. I want to introduce sync between devices of my users. Firebase DB looks like an acceptable solution, but Firebase DB<
This is not what the OP asked about, but hopefully useful to some seekers.
You can use any combination of client and server database to implement storing remotely-maintained data in the device so it will be available when offline.
SQLite
(which is using the "native" browser database, works on iOS Safari
and Android webkit browsers)
IndexdDB
(another "native" option, but not supported in early Android, or
fully supported for iOS - so NOT a good option)
JayData
(which provides an abstraction layer from the underlying native implementation)
MySQL (for an SQL DB on the server)
and, of course there are many many more.