Hi Sam...

If u are looking for Unpaid apps,Then

• askIITians
• Khan Academy
• embibe

But the paid apps are having very good content....like

• Byju's
• Topprs

askIITians: The app as the developers say is Free!! The app contains video lectures, revision notes, mind maps, study planner , NCERT Solutions etc etc. But the app didn’t have Q&A feature right now as the app is under development. Except this the app is awesome!

 Khan Academy: The app is free of cost and provides good quality video lectures, test series etc etc but the only thing they ask for is donation. If you want to donate money you can.

 Byju’s: This app is good, they are providing everything but provide Free trial upto 10–15 days only. After that you have to pay. The videos are of good quality, they also use 3D animation to teach in better way but one problem they are toooo slow.

 Topprs: The app contain everything. Best thing about the app is you can ask questions directly to the teachers and they also answer them maximum in 15 minutes but you can ask 3 free questions from them, if you want to ask questions further you have to pay.

Thank U