Datomic is a brand new kind of database. Queries runs on the client/app, not on the database server. It writes data to other databases, instead of implementing its own storage engine. It has a completely different API for reads vs. writes. And it’s single threaded (and, believe it or not, this is an amazing idea).
This will be a quick run-through of Datomic and why the aforementioned things are not just good, but great!