http://proguard.sourceforge.net/
ProGuard is a free Java class file shrinker, optimizer, obfuscator, and preverifier. It detects and removes unused classes, fields, methods, and attributes. It optimizes bytecode and removes unused instructions. It renames the remaining classes, fields, and methods using short meaningless names. Finally, it preverifies the processed code for Java 6 or for Java Micro Edition.
http://code.google.com/p/pulpcore/
http://www.interactivepulp.com/pulpcore/
PulpCore is an easy-to-use API designed to create modern-looking 2D web games with a positive user experience.
http://processing.org/
Processing is an open source programming language and environment for people who want to program images, animation, and interactions. It is used by students, artists, designers, researchers, and hobbyists for learning, prototyping, and production. It is created to teach fundamentals of computer programming within a visual context and to serve as a software sketchbook and professional production tool. Processing is an alternative to proprietary software tools in the same domain.
https://scenegraph.dev.java.net/
Welcome to the Scene Graph project, which provides "scene graph" functionality at the Java level, as well as providing one of the important runtime elements that the JavaFX Script language depends upon from the underlying platform.
http://www.13thmonkey.org/~boris/jgame/
http://slick.cokeandcode.com/
http://www.jmonkeyengine.com