What is Copyleft? 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. The
simplest way to make a program free software is to put it in the
public domain, uncopyrighted. This allows people to share the
program and their improvements, if they are so minded. But it
also allows uncooperative people to convert the program into
proprietary software. They can make changes, many or few, and
distribute the result as a proprietary product. People who
receive the program in that modified form do not have the
freedom that the original author gave them; the middleman has
stripped it away. In the GNU project, our aim is to give all
users the freedom to redistribute and change GNU software. If
middlemen could strip off the freedom, we might have many users,
but those users would not have freedom. So instead of putting
GNU software in the public domain, we “copyleft” it. Copyleft
says that anyone who redistributes the soft