Copyleft

We've all heard of Copyright, but what about Copyleft?


Basically, instead of allowing a work to fall completely into the public domain, where no ownership of copyright is claimed, copyleft allows the author to impose some restrictions on those who want to engage in activities that would usually be reserved by the copyright holder. 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 author may give every person who receives a copy of a work permission to reproduce, adapt or distribute it and require that any resulting copies or adaptations are also bound by the same licensing agreement.

While copyright law gives software the authors control over copying, distribution and modification of their works, the goal of copyleft is to give all users of the software the freedom to carry out these activities.

What are your thoughts on copyleft? More good than bad or the other way around?