Planmesh - The easiest way to plan with friends
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
tripcake - Doodle for travel plans with friends
Event Hunt - Startups and Tech Events Curated By Locals
eezy - Daily adventures for ambitious people
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets