25 years of GNU: GNU's Not Unix.
Read more about "What is free software and why is it so important for society?" @ the Free Software Foundation / FSF. See the movie in your language
I also added the FSF to the basics section, together with the wikipedia definition of copyleft. In the read section, there's a link to Lawrence Lessig's "Free culture", or "How Big Media Uses Technology and the Law to Lock Down Culture and Control Creativity". Lawrence is the founder of Creative Commons.