The .pde file is the source code in Processing, a dialect of Java that simplifies writing applets.

The .java file is Processing's translation or wrapping in Java.

The .jar file is the compiled applet.

The data directory contains a font and an image used by the applet. It must be in the same directory as the .jar file to run the applet.

-rw-r--r--   1 sw  staff  258115 Dec 30 00:22 RounderRouter.jar
-rw-r--r--   1 sw  staff    8182 Dec 30 00:21 RounderRouter.java
-rw-r--r--   1 sw  staff    7670 Dec 30 00:21 RounderRouter.pde
drwxr-xr-x   8 sw  staff     272 Dec 29 23:27 data
-rw-r--r--   1 sw  staff    2232 Dec 30 00:22 loading.gif

This ls -l style index was made with a php script.