I wish there were open source, less Clojure-centric implementations of Datomic, particularly as a plugin over something like Postgres. It has many good ideas

Datahike [0] provides similar functionality to datomic and is open source. It lacks some features however that Datomic does have [1].

[0]: https://github.com/replikativ/datahike

[1]: https://github.com/replikativ/datahike#when-to-choose-datahi...