Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
RoomForTea - A female-friendly housing network in London, UK.
Event Hunt - Startups and Tech Events Curated By Locals
tripcake - Doodle for travel plans with friends
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Magpie - Female travelers club - meet women like you when you travel