JanusGraph

JanusGraph is an open source, distributed graph database under The Linux Foundation. JanusGraph is available under the Apache License 2.0. The project is supported by IBM, Google, Hortonworks and Grakn Labs.
JanusGraph supports various storage backends (Apache Cassandra, Apache HBase, Google Cloud Bigtable, Oracle BerkeleyDB, Scylla). Scalability of JanusGraph depends on the underlying technologies, which are used with JanusGraph. For example, by using Apache Cassandra as a storage backend scaling to multiple datacenters is provided out of the box.
JanusGraph supports global graph data analytics, reporting, and ETL through integration with big data platforms (Apache Spark, Apache Giraph, Apache Hadoop).
JanusGraph supports geo, numeric range, and full-text search via external index storages (ElasticSearch, Apache Solr, Apache Lucene).
JanusGraph has native integration with the Apache TinkerPop graph stack (Gremlin graph query language, Gremlin graph server, Gremlin applications).
History.
JanusGraph is the fork of TitanDB graph database which is being developed since 2012.
Licensing and contributions.
JanusGraph is available under Apache Software License 2.0. 
For contributions an individual or an organisation must sign a CLA paper.