Some alternatives are Xamarin, ReactNative, Cordova or low level C++ libraries. There are many alternatives for making multiplatform projects or sharing code between them. Benefits over shared code across platforms That is, in fact, the purpose of this project, to help you with that conversion.

On top of that, if you consider the similarities between Swift and Kotlin, you can easily convert code in one language to the other one, and have Swift developers writing Kotlin (and vice versa) with ease. Moreover, Kotlin is fully integrated in IntelliJ (Android Studio), so you can keep using the 'de facto' IDE for Android with all the added benefits brought by Google, and it even has a Java to Kotlin converter if you want to update your legacy Java. You can check some of the benefits and differences in Kotlin official documentation and a nice list of reasons to chose Kotlin over Java. It is a pleasure to write Kotlin code, much more readable and compact that the Java counterpart. If you are a Java developer, you will find in Kotlin a much more modern and safer language (optionals and mutation).

You can check a side by side comparison of Swift and Kotlin here. It provides the most important Swift features (optionals, extensions, generics, lambdas.) and a very similar syntax. If you are a Swift developer, you will love Kotlin. It adds lots of great features while at the same time it keeps complete interop with Java, which means that you can combine them both together as you prefer. Kotlin is a great language, it is to Android/Java what Swift is to iOS/Objective-C. It comes with a desktop Mac application to copy & paste your code, as well as a command line tool to transform a complete project to Kotlin. It does string transformations as well as some more complicated ones like transforming guard statements to negative if statements, properties, memory management and many others. It applies transformations to the Swift code to get as correct as possible Kotlin code (see limitations below). SwiftKotlin is a framework, a command line tool and a Mac application for translating Swift code into Kotlin. A tool to convert Swift code to Kotlin in a very easy and quick way.

Java to kotlin conversion online