This is meant to provide a framework for Java programs that want to provide chaining of various filters, or any other example where you want to move items between an inactive list and an active list. It does some neat things, including balancing the widths of the two JLists.
The test classes are called Filters because this type of selection GUI is often used to select chained filters, but the FilterGUI is much more general than this: a list of files to include/exclude, a list of users, or a list of filters; any of these can be used.