Kotlin is a programming language over the JVM (like Java). It is well known for being the official programming language for Android. But Kotlin is a reliable and powerful programming language that can also be used for server-side applications. I have been using Kotlin for 4 years to develop server-side applications. Here are the 6 reasons why it is a great choice for building your next backend: Java is one of the vastest ecosystems in the programming world.