Virtuoso

From semanticweb.org

Virtuoso Universal Server
virtuoso.openlinksw.com
Status:	stable
Last release:	5.0.9 (Sep 16, 2008)
Affiliation:	OpenLink Software

Virtuoso Universal Server s a middleware and database engine hybrid that combines the functionality of a traditional RDBMS, ORDBMS, virtual database, Resource Description Framework (RDF), XML, free-text, Web Application Server, and File Server functionality in a single server product offering. Rather than have dedicated servers for each of the aforementioned functionality realms, Virtuoso is a "universal server"; it enables a single multithreaded server process that implements multiple protocols. The open source edition of Virtuoso Universal Server is also known as OpenLink Virtuoso.

Virtuoso is cross-platform, and available in GPL Open Source and Pay Licensed Closed Source versions.