It's meant for Java developers who lack the experience or knowledge to write a GUI themselves, but otherwise feel comfortable writing a game in Java. It might even be interesting for non-programmers who want to learn to program
The functions should be fairly clear as to their purpose, and in any case, the zip file also includes an (executable) demo that demonstrates the features of the GUI. Also, it's all written very properly, with encapsulation and all that stuff.
Questions and comments welcome!
Basic GUI
Demo GUI