Many Wt / JWt projects are about porting existing desktop applications to the web. Wt and JWt borrow their API from desktop applications and thus this usually works out really well.

FigTree is a Java Swing application with a basic UI available as a Java applet. In no more than 500 lines Java code, we’ve reimplemented the applet version as a real web application, and needed just a one line change to the existing Java Swing code!