The Xith3d project consists of powerful middleware consisting of a scenegraph and an extensible renderer. The goal is to create a lean and performative scenegraph and renderer while at the same time allowing for extensions and enchancements to all stages of the rendering pipeline.
You can think of it as a 3D engine. It allows to create games, or any application requiring a 3D visualization. It's versatile, usable with JOGL or LWJGL, embeddable in AWT, Swing, SWT (Eclipse).
It has support for physics engine (JOODE), and many development facilities.
It's fast and easy-to-use.