EmploymentCrossing.com LinkedIn, the no-frills social networking site for professionals, has added online programs from eight other companies in an attempt to compete with other social networking sites. LinkedIn’s users will be able to share book recommendations through an application created by online mega-retailer Amazon.com. Other apps include business presentation software from Google, travel itinerary tools from Tripit, and a file-management system from Box.net. Mountain View, California-based LinkedIn makes money from advertising and subscriptions to employers, head hunters and sales representatives. LinkedIn is a business-oriented social networking site founded in December 2002 and mainly used for professional networking. As of October 2008, it had more than 30 million registered users, spanning 150 industries. Rival networking sites Facebook and MySpace each have more than 100 million members.