Dimitri Fontane explains a process:
This architecture is the one the documentation lists as “consolidating multiple databases into a single one, for example for analytical purposes”. The application developer’s version: three different applications (a shop, a CRM, a billing system), each with its own schema and its own server, all feeding a warehouse; and then the warehouse’s changes exported to something that is not Postgres.
Click through for examples, as well as what limitations you’re liable to run into along the way.