Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Shapr - A completely free way to build your professional network.
Event Hunt - Startups and Tech Events Curated By Locals
GetReal - Meet new people, in person
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Mobilizon - A free and federated tool to get our events off Facebook