Bitsy graph database is described as 'Bitsy is a small, fast, embeddable, durable in-memory graph database that implements the Blueprints API. It supports ACID transactions with optimistic concurrency control and on-disk persistence'. There are eight alternatives to Bitsy graph database 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 Bitsy graph database 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.