Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Foursquare Trip Tips - Collect and share travel recommendations from friends.
Event Hunt - Startups and Tech Events Curated By Locals
Likewise - Get recommendations you love, from people you know.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Wayward - Track and share your adventures