iPhone app Listn pitches itself as a way for people to “listen to your friends’ music for free”, aggregating songs from iTunes, Rdio, Spotify, YouTube and SoundCloud into a collection that can then be shared with friends. It launched quietly in January 2013, but has now announced a $500k seed funding round. “Just like Instagram helps people share experiences through pictures, Listn connects people through music by enabling users to browse each other’s music collection, whether they are best friends or even strangers,” parent company MFive Labs’s CEO Mike Schmidt tells VentureBeat. The key here, as with a number of other recent social music apps, is that using existing streaming services as its source spares Listn from copyright licensing headaches, although that doesn’t mean the company has an obviously-successful business model lined up. There’s merit to apps and services that sit in between the various streaming music services connecting them, but figuring out how to make money from that will be the challenge for Listn and its rivals.