Free software was the beginning of the „open movement“. The founder of the Free Software Foundation (FSF), Richard Stallman, realized early, that who controls the software, can exercise control over the dissemination of information, and impede technical innovation; in short, gain enormous power. He therefore demanded, that all software should be free (free as in freedom, not in free beer) and source-codes should be open to allow anyone to adapt programs to his or her needs, and to ensure quick detection of bugs, and rapid interception of espionage operations. Today, a large part of server software is already licensed as free software and is open-source. Only in end-user applications and in public administration proprietary operating systems (like Windows or Mac OS X) still dominate the market. The free-software movement has also led to a new mode of production, the so-called „peer-to-peer production“. In this process many people work cooperatively, on a level playing field, often without a leader, and usually without pay, to generate high-quality software. In this lecture the most exciting examples of free software for private and professional use are presented.