Distributed Graph Database
Titan is a highly scalable "graph database":http://en.wikipedia.org/wiki/Graph_database optimized for storing and querying large graphs with billions of vertices and edges distributed across a multi-machine cluster. Titan is a transactional database that can support thousands of concurrent users, complex traversals, and analytic graph queries.
h2. Learn More
The "project homepage":http://titandb.io contains more information on Titan and provides links to documentation, getting-started guides and release downloads.