This sounds like a job for CouchDB with PouchDB in-client. You'll need to configure replication per-db, but this can be scripted via cURL or wget, as CouchDB ha

This sounds like a job for CouchDB with PouchDB in-client. You'll need to configure replication per-db, but this can be scripted via cURL or wget, as CouchDB has a REST API. That's precisely what this system was designed for.