Well Kotlin is basically a drop-in replacement for Java. You can literally create a Kotlin project in Intellij IDEA (Community Edition), drop in some jars (and

Well Kotlin is basically a drop-in replacement for Java. You can literally create a Kotlin project in Intellij IDEA (Community Edition), drop in some jars (and compiled native lib if required), and you get full completion to every class, and everything 'just works'. So the obvious choices would be LibGDX and Lwjgl 3 (which is written mostly in Kotlin). As for tutorials, it's close enough to Java that you can rewrite anything pretty much word for word (albeit with a slightly different syntax), and there's a Java -> Kotlin translator in IDEA. It keeps the semantics very close to Java, but with some sugar and niceties. It really is the 'Java replacement' that languages like Scala and Ceylon attempted to be.