They're not really set up for taking external contributions, but there's nothing stopping you from making videos and putting them on YouTube. If you pick a subj

They're not really set up for taking external contributions, but there's nothing stopping you from making videos and putting them on YouTube. If you pick a subject and do it better than anyone else, you will have made a valuable contribution. I know that's not as cool as contributing to Khan Academy, and makes it harder to get an audience, but it's something you can do at any time, without asking permission from anyone.