I need to clarify this.

Anyone can contribute, but you can’t use the material within a commercial context (a very common scenario) under the NC license.

On the other hand, khana might give you a special license for particular commercial use if you want to take your chances with that, and it is generally a good thing more people are trying to provide organized free visual lessons for society.

I want to mention stackoverflow. They provide a P2P download of the entire contents of the site and use CC-by-SA (last time I checked) which is sort of like a weaker version of the GPL.

I have been interested in a while for producing tutorials on lots of topics (including the source code to the tutorials/videos) and using open source licenses. Although I will eventually get going on this, I would be happy to know of similar efforts out there. I though I might want to leverage ka but won’t as long as they use that license.