Foursquare - Foursquare is all about helping you find new ways to explore your city.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Tripadvisor - The Tripadvisor mobile app is available for the Android and iOS platforms. It can be used to create reviews of hotels, restaurants, and to chat with other travelers on Tripadvisor forums.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Yellow Pages - YP.com local search connects you with over 19 million local businesses.
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.