Btw Datomic is free now that Nubank supports it (and runs a large bank on it).

There's also a fantastic kind of mini, FOSS, file-based Datomic-style Datalog DB that's not immutable called Datalevin. Uses the hyper-fast LMDB under the hood. It's called Datalevin. https://github.com/juji-io/datalevin