An example would be DBPedia, a service that extracts data fro m Wikipedia and makes it machine readable via SPARQL (language similar to SQL).

For instance, here is what Wikipedia has to say about Triplestore:

https://en.wikipedia.org/wiki/Triplestore

And here is DBPedia representation of it:

http://dbpedia.org/page/Triplestore

And here's how you'd get the data from DBPedia programmatically using SPARQL -

select * where { <http://dbpedia.org/resource/Triplestore> ?p ?o. }

Try it here - http://dbpedia.org/sparql/