What is kotlin

Kotlin is a general purpose, statically type and open-source programming language. It runs on JVM and can be used anywhere, there Java is used today. It can be used to develop Android apps, server side apps and much more.

History of Kotlin
Kotlin was developed by JetBrains team. A project was started in 2010 to develop the language and officialy, first released on Fabruary 2016. Kotlin was developed under the apache 2.0 license.

Features of Kotlin
Concise: Kotlin reduces writing the extra codes. This make Kotlin more concise.
Null safety: Kotlin is null safety language. Kotlin aimed to eliminate the NullPointerException (null reference) from the code.Interoperable:
Interoperable: Kotlin easily calls the Java code in a natural way as well as Kotlin code can be used by Java.
Smart cast: It explicitly typecasts the immutable values and inserts the value in its safe cast automatically.
Compilation Time: It has better performance and fast compilation time.
Tool-friendly: Kotlin programs are build using command line as well as any of Java IDE.
Extension function: Kotlin supports extension functions and extension properties. Which means it helps to extend the functionality of classes without touching their code.

Using Kotlin for Android Development
Kotlin is a great fit for developing Android applications, bringing all of the advantages of a modern language to the Android platform without introducing any new restrictions:

Compatibility: Kotlin is fully compatible with JDK 6, ensuring that Kotlin applications can run on older Android devices with no issues. The Kotlin tooling is fully supported in Android Studio and compatible with the Android build system.
Performance: A Kotlin application runs as fast as an equivalent Java one, thanks to very similar bytecode structure. With Kotlin's support for inline functions, code using lambdas often runs even faster than the same code written in Java.
Interoperability: Kotlin is 100% interoperable with Java, allowing to use all existing Android libraries in a Kotlin application. This includes annotation processing, so databinding and Dagger work too.
Footprint: Kotlin has a very compact runtime library, which can be further reduced through the use of ProGuard. In a real application, the Kotlin runtime adds only a few hundred methods and less than 100K to the size of the .apk file.
Compilation Time: Kotlin supports efficient incremental compilation, so while there's some additional overhead for clean builds, incremental builds are usually as fast or faster than with Java.
Learning Curve: For a Java developer, getting started with Kotlin is very easy. The automated Java to Kotlin converter included in the Kotlin plugin helps with the first steps. Kotlin Koans offer a guide through the key features of the language with a series of interactive exercises.