Blazegraph

Blazegraph (formerly known as BigData) is a graph database with support for the Blueprints and RDF/SPARQL APIs[1]. Blueprints is analogous to the JDBC, but for graph databases[2]. SPARQL is a query language for RDF[3].

Blazegraph is freely available under the GPLv2 open-source license[4]. Commercial licenses are also available.

One of the more touted features of Blazegraph is that "it supports up to 50 Billion edges on a single machine and has a High Availability and Scale-out architecture."[1]

tamsin woo has written an Ruby gem for connecting with Blazegraph: https://github.com/ruby-rdf/rdf-blazegraph

Cornell has a nice document on how to get started with Blazegraph: https://confluence.cornell.edu/display/~elr37/Blaze+Graph+and+ActiveTriples

I've posted my first examples using Blazegraph standalone on this GitHub repo: https://github.com/hectorcorrea/blazegraph_demo

[1] https://www.blazegraph.com/product/
[2] https://github.com/tinkerpop/blueprints/wiki
[3] https://www.w3.org/TR/rdf-sparql-query/
[4] https://www.blazegraph.com/services/blazegraph-licensing/