DBpedia is a web tool built to extract structured information from Wikipedia, convert it into RDF, and make it freely available on the Web. In a nutshell, DBpedia is the Semantic Web mirror of Wikipedia.
The DBpedia Spotlight API is a RESTful API tool for annotating mentions of DBpedia resources in text, providing a solution for linking unstructured information sources to the Linked Open Data cloud. DBpedia Spotlight performs named entity extraction, including entity detection and Name Resolution. At this time, the DBpedia Spotlight API is free and requires no sign up or registration to use.