Is javafx used for developing only system apps?

Answer 1

The original goal of the Java Platform was to provide a software environment for embedded devices. However, a strange loop in history made Java the number one development language for enterprise software. Java on the client received less attention than the lucrative server-market. With JavaFX, the Java platform now has a strong client component that can be used to develop applications for desktops, tablets, mobile and embedded systems.
The new Java Client component, JavaFX, has been designed from scratch, taking into account experiences from both the Java world as well as from other UI frameworks. One of the key principles of JavaFX is to leverage hardware (e.g. GPU's) as much as possible. Indeed, a requirement for todays user interfaces is a highly responsive and performant toolkit.
It's like Christmas. 😇

Answer 2

JavaFX isn't really used by anyone, I had to write this reply after seeing Vipul's answer which is dangerously misleading to people who are trying to learn. See this analysis of the status of JavaFX: http://www.codenameone.com/blog/should-oracle-spring-clean-javafx.html

It's effectively dead. The mobile "effort" is done by an external startup. I tried their JavaOne app on my iphone and it was the crashiest slowest thing I ever tried. It made phonegap apps look good.