Kotlin 1.0 Released: Pragmatic Language for JVM and Android
actually I'm still unsure about kotlin. some things are really great some things are not. I mean i will still use kotlin, especially for libraries since it is great for that. however somehow I still missed something on top of Executors and CompletionStage. And I'm totally unhappy about "So, why doesn’t Kotlin have its own package manager, or its own build system?  Because there’s already Maven and Gradle, and re-using their huge number of plugins is crucial for many projects."
The answer would be totally valid, however people who worked with maven, gradle, ant or even sbt (which isn't offically supported) could be unhappy. all of these build systems are useful, but not actually great. I mean you could work with them but it's not actually great to use them.