What book would you recommend to someone who has decent experience in Java but wants to learn Kotlin? I saw Bruce Eckel is writing a book but it’s not finished yet sadly.

I've heard Venkat's book is quite good - https://pragprog.com/book/vskotlin/programming-kotlin

That was the book I bought, also coming from Java. Content is solid. Did not like the very conversational style that much. It feels like it could have been half the page count with the same content. One specific point: Collection transformations are not handled at all.

https://www.manning.com/books/kotlin-in-action of course!