Freebase – Open Graph Database with More Than 23 million Entities
http://wiki.freebase.com/wiki/Main_Page

An entity is a single person, place, or thing. Freebase connects entities together as a graph. Ways to use Freebase: a) Use Freebase’s Ids to uniquely identify entities anywhere on the web; b) Query Freebase’s data using MQL; and c) Build applications using our API or Acre, our hosted development platform. Freebase is also a community of thousands of data-lovers, working together to improve Freebase’s data. Learn how to contribute, join our mailing list, or find out more on our community page. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog. This has been added to Business Intelligence Resources Subject Tracer™ Information Blog. This has been added to Knowledge Discovery Subject Tracer™ Information Blog.