JavaFX was meant to replace Swing, but it isn't really a newer version of Swing. More like a completely new framework built with modern concepts. It's pretty awesome.
TornadoFX is a little more than the Kotlin version of JavaFX, more like a framework built on top of JavaFX. It does a lot of the standard Kotlin wrapper library things like remove boilerplate and add some DSLs, but there's more to it than that. It basically takes a lot of the most common workflows and builds standard implementations for them, such as injected views/controllers, data models and validation, animation helpers, etc. You can check out the guide for more info:
https://edvin.gitbooks.io/tornadofx-guide/