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DBpedia is a community effort to extract structured information from Wikipedia and to make this information available on the Web. It is a fine example of the next generation semantic applications and can be compared by functionality to Freebase which also uses Wikipedia's dataset. The difference is that DBpedia's data and framework are open-source, and it is built using W3C standards such as RDF/OWL and SPARQL.

DBpedia makes it possible to ask sophisticated queries, such as as to select “people influenced by Friedrich Nietzsche” or “German musicians who were born in Berlin”. The second query looks like this in SPARQL (prefixes omitted):

SELECT ?name ?birth ?description ?person WHERE {
     ?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin> .
     ?person skos:subject <http://dbpedia.org/resource/Category:German_musicians> .
     ?person dbpedia2:birth ?birth .
     ?person foaf:name ?name .
     ?person rdfs:comment ?description .
     FILTER (LANG(?description) = 'en') .
}
ORDER BY ?name

It can be executed using one of the several SPARQL endpoints (see results here).

The datasets, now containing 103 million triples that describe 1.95 million things, are published online as linked data and can be browsed using semantic browsers such as Tabulator. They are also available for download.
What is even more exciting, DBpedia is also being linked to different other semantic datasets such as MusicBrainz (information about music and artists) and GeoNames (information about geographical features), becoming the core of W3C's Linking Open Data project.