Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
WhosDown - App where you can genuinely make friends—connecting with someone that shares a common interest
Event Hunt - Startups and Tech Events Curated By Locals
Open Cult - A place for people with common interests to meet IRL.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Speciface - Instant access to contact information of people nearby