Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Everfest - A global calendar and search engine for festivals
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Find your best festival - Compare the music you follow with 100s of festival lineups
Bigtent - BigTent is a web-based organization and communication portal for groups.
Hootenanny - Find music festivals featuring artists you love.