Neo4j: World's Leading Graph Database. Neo4j. Neo4j version 1.0 was released in February, 2010.[4] The community edition of the database is licensed under the free GNU General Public License (GPL) v3.
The additional modules, such as online backup and high availability, are licensed under the free Affero General Public License (AGPL) v3. The database, with the additional modules, is also available under a commercial license, in a dual license model.[5] Neo4j version 2.0 was released in December, 2013.[6] Titan. Titan is a scalable graph database optimized for storing and querying graphs containing hundreds of billions of vertices and edges distributed across a multi-machine cluster.
Titan is a transactional database that can support thousands of concurrent users executing complex graph traversals in real time. In addition, Titan provides the following features: