Spotify - Map shows when two people play same song at same time
POP (Prototyping on Paper) - POP helps you make interactive prototype with ease. If you can draw, you can design apps.
SoundCloud - Enjoy music & follow favourite artists
Invision - Prototyping and collaboration for design teams
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.