AllegroGraph is a closed source triplestore which is designed to store RDF triples, a standard format for Linked Data.[2] AllegroGraph is currently in use in Open source projects,[3] commercial projects[4][5][6][7] and Department of Defense projects.[8] It is also the storage component for the TwitLogic project[9] that is bringing the Semantic Web to Twitter data.[10]


AllegroGraph® is a modern, high-performance, persistent graph database. AllegroGraph uses efficient memory utilization in combination with disk-based storage, enabling it to scale to billions of quads while maintaining superior performance. AllegroGraph supports SPARQL, RDFS++, and Prolog reasoning from numerous client applications.
http://franz.com/agraph/allegrograph/
http://allegrograph.com/