It is the Java version of XAML, and it is quite nice to use, but the uptake has been on the slow side. There were quite a few sessions at JavaONE 2016:

https://oracle.rainfocus.com/scripts/catalog/oow16.jsp?event...

Probably the place where it has seen more uptake has been in car infotainment systems, like by Volkswagen.

https://static.rainfocus.com/oracle/oow16/sess/1462531766187...

However our Java desktop native projects are still mostly Swing based, or make use of either Eclipse or Netbeans as desktop framework.

And of course there is the Android Java fork, which doesn't offer any JavaFX compatibility (some guys on the community are porting it though).