Nightout - The standard in event ticketing and marketing by NIGHTOUT

Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Airbnb - Book unique places to stay and things to do.

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

TickPick - Purchase tickets to your favorite events with no hidden fees

Bigtent - BigTent is a web-based organization and communication portal for groups.