Ibis paint X is very popular and versatile drawing app. I usually draw illustration on this app. This is very good app for doing digital art like illustration, mandala etc. And it is free app and   its premium version is also available.  And we can draw something on our phone also and for drawing something it is not necessary to have tablet or iPad. This app is available for Android also. We don't have to buy a paid version of this . Digital painting become so much easier . In this app there is a tutorial feature that help to know the app how it works.