I'll just throw a note for a new product, AWS's QLDB. It's an internal managed product that combines a replicated, immutable, versioned document database with ACID transactions and an immutable, provable history of every modification. There's some streaming and subset SQL on the back end.

Something this focused should have a few applications where bit level auditability matters, eg financial, chain of events, etc. Of course it comes with some tradeoffs vs a relational or kv db.

I wonder if there would be room for a self-hosted clone?