I've heard Datomic was made by Clojure people and is really good software too, though unfortunately proprietary.

All of those things are true. If you want to check out Datalog-using DBs in Clojure that are open source, here are two alternatives:

* Datahike (similar to Datomic but similar): https://github.com/replikativ/datahike

* Crux (a bitemporal graph database): https://opencrux.com

Have you checked pldb/db-rel from core.logic?

I haven't started checking the library yet... But I have it on my radar, since I'm already doing clojure I feel like it is an easy way to "add some prolog" to my programs :-)