In August 1991 Tim Berner-Lee announced the birth of WWW technology and encouraged scientists to adopt and develop it. Soon after, those programs, along with their source code, were made available to people interested in their usage. In practice CERN informally allowed other people, including developers, etc., to play with and maybe further develop what it has been made till that moment. This was the official birth of CERN httpd. Since then Berner-Lee started promoting the adoption and the usage of those programs along with their porting to other OSs.
