It was four years ago when I discovered Khan Academy, which as far as I can remember a Youtube channel with more than a thousand videos. If I am not mistaken, it was only then managed by Salman Khan, it’s founder.
A year ago or two, when I searched the internet, I learned that Khan Academy has already its own website and it is run already by a group of educators. Three weeks ago, I started using the website. As of this writing, I have already watched 29 videos (oh yes, I watched them from start to end) and earned 56,340 points. 🙂 » Read more