I subscribed for this website and got a very good knowledge on what I want. It got every topic that a student needs to learn.
1.Math
2.Physics
3.Chemistry
4.economy
5.astrophysics and also training for many other competive exams like SAT, MCAT, GMAT, NCLEX-RX, CAHSEE and also for IIT JEE. The greatest part is that you can save it offline, all the videos, notes etc.
They often give test which includes formula and calculation. This type of interactive coaching is kinda fun and This is also available as an app is GOOGLE PLAY which is absolutely FREE.
This website is available in 36 LANGUAGES.
The test you write is scored with energy points which is very attractive and encouraging for small kids. There is NO AGE LIMIT in this website to learn. Even the student knows nothing the teachers in the videos and with those tests the student can become a pro in that subject.