1. Apache Accumulo, July 2020. https://accumulo.apache.org/
2. Apache HBase, July 2020. http://hbase.apache.org/
3. Gelly: Flink Graph API, July 2020. https://ci.apache.org/projects/flink/flink-docs-stable/dev/libs/gelly/
4. JanusGraph, July 2020. https://janusgraph.org/
5. OrientDB Community, July 2020. http://www.orientechnologies.com/orientdb/