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FigTree is an application created by Andrew Rambaut for visualizing phylogenetic trees estimated from molecular data. It is a Java Swing application with a basic UI available as a Java applet.
In no more than 500 lines Java code, we rehashed the applet version into a real web application, reusing much of the existing application. In fact, we needed only a single line code change in the reused Swing code.
The source code of this example is not part of the JWt source distribution, but you can find it (including the web version which we contributed) on the FigTree project page.
See also our blog post on porting this application.