Creative Commons
Creative Commons licenses help creators retain copyright while allowing others to copy, distribute, and make some uses of their work, at least non-commercially.
All of the Creative Commons licenses require that users provide attribution to the creator when the material is used and shared. Some licensors choose the attribution requirement as the only condition for reuse of the material; this is designated as the BY license. The other five licenses combine the BY license with one or more of three additional license elements: NonCommercial (NC), which prohibits commercial use of the material; NoDerivatives (ND), which prohibits the sharing of adaptations of the material; and ShareAlike (SA), which requires adaptations of the material be released under the same license. (Adapted from http://wiki.creativecommons.org/ FAQ#What_are_Creative_Commons_licenses.3F.)