I just read about this on the New Scientist web site. The copyleft is the strange cousin of a copyright and it sort of a movement supporting the complete sharing of thoughts and writings. It certainly puts plagiarism in a different light.
http://www.newscientist.com/hottopics/copyleft/

The article mentions the Wikipedia (http://www.wikipedia.com), which is basically an online encylopedia to which anyone can contribute. If you see an article that's missing, or needs correcting, you can go ahead and change it. It's fairly new, but growing fast and the creators are hoping that it will turn into a huge, respectable resource.