Atomic Kotlin is the book explaining Kotlin to both novices and experienced programmers. It doesn't rely on prior Java experience which makes it different from many of the currently available resources on Kotlin.
The book isn't yet finished, but you can read the current version. The book is accompanied by the course: a set of small exercises with automatic checking and available answers. Read about to course installation here: http://atomickotlin.com/exercises/.
Check http://atomickotlin.com/ to get the full information about the book.