Kotlin looks very nice. But I think there are languages with better concurrency support - Elixir (cheap green threads in the VM) and Scala (actors and futures)

Kotlin looks very nice. But I think there are languages with better concurrency support - Elixir (cheap green threads in the VM) and Scala (actors and futures) come to mind. I think it really depends on your use case too. Kotlin is great for mobile apps and games, where coroutines are fantastic (see also C#/Unity there). For writing scalable web services, you need more control and resilience. There Elixir and Scala are the heavyweights.