In essence, JetBrains has caught up to where Xamarin was prior to the announcement of Xamarin.Forms: the ability from one solution to have separate iOS and Android UI applications with a business logic library shared between the two, all written in C# or F# (the two languages supported by the Mono compiler). The main difference is that one of the vendors actually supports the language in question (Kotlin) as a first-class citizen.
And going the other way, there's been noise for a couple years that Android apps could be written in Swift, achieving the same effect in reverse.