The fact that PostgreSQL is pigeon-holed as a "database" blinds folks to the fact that it is also a full-fledged integration environment. It's a place where you can bind together multiple kinds of data and multiple kinds of application.

* Use FDW connections to pull in data from all kinds of sources! Multiple databases, file formats, HTTP buckets, you name it!

* Custom behaviours in multiple languages! PL/Python, PL/Perl, PL/R!

* Read and write to web services! (PL/Python, pgsql-http)

* And now string together arbitrary containers! (pgpodman)

The way the extension system and the type system play together, it really is a very generic place to build weird integrated systems.