Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Mightybell - Build a community and a business on mobile
Facebook Local - Discover places to go and events happening near you
MyTalk - Build a community around your product
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Hey.Cafe - Hey.Café is a social network built around communities called cafés.