Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Spotify - Map shows when two people play same song at same time
Event Hunt - Startups and Tech Events Curated By Locals
tradiio - Reward-based music discovery app
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Magic Playlist - Get the playlist of your dreams based on a song