https://bmeg.github.io/grip/

GRIP stands for GRaph Integration Platform. It provides a graph interface on top of a variety of existing database technologies including: MongoDB, Elasticsearch, PostgreSQL, MySQL, MariaDB, Badger, and LevelDB.

Properties of an GRIP graph:

• Both vertices and edges in a graph can have any number of properties associated with them.
• There are many types of vertices and edges in a graph. Thus two vertices may have myriad types of edges connecting them reflecting myriad types of relationships.
• Edges in the graph are directed, meaning they have a source and destination.

GRIP also provides a query API for the traversing, analyzing and manipulating your graphs. Its syntax is inspired by Apache TinkerPop. Learn more here.