Spotify may be one of the more successful streaming music services around, but man, the company is tweaking and adding features like it has something to prove. Spotify’s only been available in the U.S. since this summer, and since then, they’ve added mandatory Facebook registration for rookie users (which kind of sucks) and six months of free, unlimited tunes for newcomers (which is awesome). Last week, CEO Daniel Ek promised a big change was coming to Spotify, and today, he unveiled it: external devs can now create apps that link in to the service using "The Spotify Platform."