Shared Spotify - Find the common songs you have between friends
Songlink - Share music with anyone.
Spotify Codes - Share codes for songs, artists, and playlists from Spotify
humit - A social networking app for music sharing and discovery.
Bands on a Budget - Economical SWAG meant for bands, often hijacked by startups
aux.app - A free web-based music platform to play music from other popular online streaming services.