Triplestores

A triplestore or RDF store is a purpose-built database for the storage and retrieval of triples through semantic queries. A triple is a data entity composed of subject–predicate–object, like "Bob is 35" (i.e., Bob's age measured in years is 35) or "Bob knows Fred".

open source semantic web framework for Java

Blazegraph is an open source triplestore and graph database,