The key features of Kotlin are as follows:

• Interoperability with Java: The most important feature of Kotlin is its deep interoperability with Java. Kotlin compiles to JVM bytecode and runs on the JVM, using Java libraries and tools.
• Concise: Unlike Java, which is verbose, Kotlin reduces the amount of boilerplate code. This results in a leaner code syntax and improved readability.
• Safe: Kotlin improves code safety through the proper initialization of properties, null safety, and strong type inference.
• No runtime overhead: Kotlin imposes no runtime overhead. The standard Kotlin library is small. The Kotlin runtime exists only to support the language features. It has mostly focused on extensions to the Java standard library. Many of its internal functions are inline.
• Collections: In Kotlin, we have higher-order functions, lambda expressions, operator overloading, lazy evaluation, and lots of other useful functions for working with collections.
• Extension functions: Kotlin allows us to extend the functionality of existing classes without inheriting from them. Extensions do not modify classes; they extend them and are resolved statically.
• Open source: Kotlin is an open-source programming language. The Kotlin project is open-sourced under the Apache 2.0 license. It is on GitHub and is open for community contribution.