As explained on the GNU website: "Copyleft is a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well. (...) Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. Copyleft guarantees that every user has freedom. (...) Copyleft is a way of using of the copyright on the program. It doesn't mean abandoning the copyright; in fact, doing so would make copyleft impossible. The word 'left' in 'copyleft' is not a reference to the verb 'to leave' — only to the direction which is the inverse of 'right'. (...) The GNU Free Documentation License (FDL) is a form of copyleft intended for use on a manual, textbook or other document to assure everyone the effective freedom to copy and redistribute it, with or without modifications, either commercially or non commercially." Creative Commons (CC) was founded in 2001 by Lawrence Lessing, a professor at Stanford Law School, California. As explained on its website: "Creative Commons is a nonprofit corporation dedicated to making it easier for people to share and build upon the work of others, consistent with the rules of copyright. We provide free licenses and other legal tools to mark creative work with the freedom the creator wants it to carry, so others can share, remix, use commercially, or any combination thereof." There were one million Creative Commons licensed works in 2003, 4.7 million licensed works in 2004, 20 million licensed works in 2005, 50 million licensed works in 2006, 90 million licensed works in 2007, and 130 million licensed works in 2008. Science Commons was founded in 2005. As explained on its website: "Science Commons designs strategies and tools for faster, more efficient web-enabled scientific research. We identify unnecessary barriers to research, craft policy guidelines and legal agreements to lower those barriers, and develop technology to make research, data and materials easier to find and use. Our goal is to speed the translation of data into discovery — unlocking the value of research so more people can benefit from the work scientists are doing." ccLearn was founded in 2007. As explained on its website: "ccLearn is a division of Creative Commons dedicated to realizing the full potential of the internet to support open learning and open educational resources. Our mission is to minimize legal, technical, and social barriers to sharing and reuse of educational materials." 2002: A WEB OF KNOWLEDGE = [Overview]