According to Wikipedia:
LinkedIn (pronounced /ˌlɪŋkt.ˈɪn/) is a business-oriented social networking site. Founded in December 2002 and launched in May 2003, it is mainly used for professional networking. As of 9 August 2010, LinkedIn had more than 75 million registered users, spanning more than 200 countries and territories worldwide. The site is available in English, French, German, Italian, Portuguese and Spanish.
LinkedIn allows members to create groups, within which discussion board functionality is available.