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I absolutely love this site. It's such an nice surprise that you suggested it, I did not know that it's this popular. I used it for math and physics. :)
This site is free as well.
apparently, it works only in US and Cn.
That's strange :(. It's an educational site, it's no threat to anybody. oh well... what about the youtube link?
No problems :). It's the site I use. I have completed quite a number of lessons. If I find anything else that is relevant and useful, I will post a link to it.