Songlink - Share music with anyone.
Songstack - Swipe to discover new music for Spotify
humit - A social networking app for music sharing and discovery.
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
aux.app - A free web-based music platform to play music from other popular online streaming services.
22tracks - DJ curated Spotify playlists on iOS