XTDB is a very interesting database to me. Not only is it distributed, but the 'bi-temporality' which is mentioned on this page means that it has essentially a

XTDB is a very interesting database to me. Not only is it distributed, but the 'bi-temporality' which is mentioned on this page means that it has essentially a built-in audit trail mechanism. I'm working on writing an RDF library for Clojure, and am looking forward to seeing whether XTDB really is as good as an RDF datastore as I suspect it is!