I posted a question in the comment group[1] of Khan Academy[2], a great education website. In fact in this page on the wiki of the site[3] under "Our Principles: the rules of the game", is said: "Openness. [...] Open content means that all content distributed by or through the Khan Academy uses the CC-by-sa license (or a compatible license) [...]" but actually in the footer of every page the is indicated a CC-3.0-NC-BY-SA license. So there must be a mistake somewhere, the point being that CC-BY-SA license would be compatible with Wikipedia and the other projects, which I think would be a great, valuable thing. Can somebody help me to clarify this point? I think it's important. Cristian [1]http://groups.google.com/group/khan-academy-comments/browse_thread/thread… [2]www.khanacademy.org [3]https://sites.google.com/a/khanacademy.org/forge/home/mission-principles-…