The app which I love most in regard of studying is meritnation.
This app help me alot in studying, when I was in class 10, I never go tution, I use to do self study.
And this is the only website which help me to pass HSLC Examination with good numbers.
I use to see videos of this site, they explain things so good, that one can easily understand any concept. There service is also very good. The have solution for all programs, they provide there solution in NCERT app which is great app for students.
They also provide videos on youtube which are very knowledgeable.And the way of explaing is also good.
OVERALL BEST APP FOR LEARNING,
KNOWLEDGE IS POWER.