There's no doubt that Wikipedia is a giant store of information. And yes, they have an API, but the data isn't exactly structured. But that didn't stop Jim Blackler, who created Quizipedia, a fun game based off of Wikipedia entries.
The Wikilocation API has expanded to include 36 languages. The geo API for Wikipedia allows developers to find articles with subjects near a specific location. With the new languages, there are now over 3.8 million geocoded articles available via this unofficial API from developer Ben Dodson.