Kotlin is a language developed by JetBrains (who develop the Intellij Idea IDE). It aims to be an alternative to Java on the JVM and is developed so it will be easily supported by an IDE (obviously it will be supported by Idea very well)
Enthusiasm is overrated. Developers who get religious with their programming language is something I can’t understand... Religion, you know, blinds people...
Scala has its limits. Some things cannot be done easily. The thing about Scala is that it makes people believe they can do anything with it, they are then frustrated when they can't. The scala-complexity blog post for example, tries to create a method that will work on collections, Java's strings and Java's arrays. Seamlessly. This is something you wouldn't even dream of doing in Java (Note: it is in fact possible to do it.)