Flockdb is described as 'FlockDB is a distributed graph database for storing adjancency lists, with goals of supporting: a high rate of add/update/remove operations potientially complex set arithmetic queries paging through query result sets containing millions of entries ability to'. There are eight alternatives to Flockdb for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and Self-Hosted solutions. The best alternative is neo4j, which is both free and Open Source. Other great apps like Flockdb are RedisGraph (Free, Open Source), Structr (Free, Open Source), NetworkX (Free, Open Source) and LemonGraph (Free, Open Source).
RedisGraph is a property graph database module for Redis. It is the first graph database to use linear algebra on sparse adjacency matrices to implement graph operations, which lets it achieve high performance. It understands OpenCypher queries.