YouTrackDB is a general-use object-oriented graph database

YouTrackDB is a general-use object-oriented graph database developed and supported by JetBrains that is already used in production internally. Key features include O(1) link traversal complexity without expensive JOINs, an object-oriented API with inheritance and polymorphism at the database level, snapshot isolation by default, and support for both Gremlin query language and TinkerPop API. The project also offers YQL (YouTrackDB Query Language), a SQL-based query language with graph extensions designed for optimal query performance.