Neo4j

Neo4j is a graph database that stores data as a labelled property graph of nodes and relationships, traversing those connections directly in memory rather than joining tables at query time. Cypher is its query language, indexes and a cost-based planner keep multi-hop lookups fast, and full ACID transactions apply to graph writes.

Teams use it for recommendations, fraud and risk analysis, IT and network topology, and knowledge graphs where the relationships carry the meaning.

The service can you a ready instance on your own hardware, so the relationship data stays on premises with no usage-based pricing and simple snapshot and restore.