What is Kotlin used for
Kotlin is designed to run on a Java Virtual Machine and can run side by side with Java. Although Kotlin first started as a language for Android development specifically, it quickly spread through the Java community because of its features and has since been used for many types of applications.
Android Development
As we mentioned, Kotlin is the preferred language for Android development as it allows developers to write more concise, expressive, and safer code. The official IDE for Android development, Android Studio, supports it completely, so you can get the same type of code completion and type checking to help you write Kotlin code as you do with Java.
Having a mobile presence is a requirement for most businesses since most people access the internet now through mobile phones. Android accounts for over 70% of the market share of mobile phones, so even if Kotlin was only for Android development, Kotlin developers would be in high demand. Still, it can be used for so much more.
Back-end web development
A lot of back-end web development is done in Java, using frameworks like Spring. But, Kotlin made inroads into server-side web development since it was so much easier for developers to work with.
The modern features of the language make it possible for Web Developers to build applications that can scale quickly on commodity hardware. Since Kotlin is interoperable with Java, you can slowly migrate an application to use Kotlin one file at a time while the rest of the application still uses Java.
Kotlin also works with Spring and other frameworks, so switching to Kotlin doesn't mean you have to change everything you're used to. Google, Amazon, and many other companies have already replaced Java with Kotlin in some of their server-side code.
Full-stack web development
It makes sense to use Kotlin for server-side web development. After all, Java has been used since its inception. Still, you can also use Kotlin for front-end development using Kotlin/JS.
Kotlin/JS allows developers to access powerful browser and web APIs in a type-safe fashion. Full-Stack Developers only need to know Kotlin. They can write front-end code in the same language that they used for back-end code, and it'll be compiled to JavaScript to run in the browser.