EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Spotify - Map shows when two people play same song at same time
Meludia - Listening exercises and to sharpen your ear and music theory skills
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
Perfect Ear - A simple yet advanced application for improving your solfege skills.
SoundCloud - Enjoy music & follow favourite artists