Marc Lowell Andreessen is an American entrepreneur, investor, and software engineer. He is the co-author of Mosaic, the first widely used Web browser; co-founder of Netscape; and co-founder and general partner of Silicon Valley venture capital firm Andreessen Horowitz. He founded and later sold the software company Opsware to Hewlett-Packard. Andreessen is also a co-founder of Ning, a company that provides a platform for social networking websites. He sits on the board of directors of Facebook,