JetBrains' alternative language for the Java platform, Kotlin – which the company has been developing since 2010 and revealed in July 2011 – has now been released as open source under an Apache 2 licence. The released tools include the Kotlin compiler, "Kompiler", a set of enhancements to standard Java libraries such as convenience utilities for JDK collections, build tools (for Ant, Maven and Gradle), and an IntelliJ IDEA plugin so it works with JetBrains' own IDE.

Kotlin, the language, is a statically typed programming language which can be compiled to Java JVM byte code or to JavaScript. It was designed to be safer than Java with static checking for problems such as null pointer dereferencing, and more concise than Java by including type inference, higher-order functions, mixins and delegation.

The developers also say they aimed to make it "way simpler than the most mature competitor – Scala". The developers have published comparisons with Java and with Scala to further explain their language's design. A Kotlin web demo allows developers to experiment with the language from their browser.

Currently the Kompiler only emits JVM byte code; JetBrains have started developing a JavaScript backend and are looking to create an LLVM backend in the future. The JetBrains developers are looking for "Kontributers" to join the project, either by working directly on the Kotlin code or by fixing other Java libraries and making them "Kotlin friendly". Snapshot builds are available to download from the project's github repository and the source is available to check out from the same repository.

The Kotlin name refers to a Russian island west of Saint Petersberg; JetBrains has a main development office in the city.

(djwm)