Creative Commons
is a nonprofit organization dedicated to making it easier for people to share and build upon the work of others, consistent with the rules of copyright.
CC provides free licenses and other legal tools to mark a creative work with the freedom the creator wants it to carry. Others can share, remix, and use commercially, depending on the terms the creator chooses.
http://creativecommons.org/aboutAttribution
Lets others copy, distribute, display, and perform a copyrighted work — and derivative works based upon it — but only if they give credit the way the original creator requests.
Noncommercial
Lets others copy, distribute, display, and perform a work — and derivative works based upon it — but for non-commercial purposes only.
Share Alike
Allows others to distribute derivative works only under the same license as the original work.
No Derivative Works
Lets others copy, distribute, display, and perform only verbatim copies of a work, and not derivative works based upon it.