Photon is a Java ray tracing (or path tracing) library that could be used to produce realistic 3D images. I started writing this library to exercise the concepts learned from the Ray Tracing in One Weekend book series. It is still so much a work in progress.
Examples of images generated by this library could be found here. This is one such example:
The above example was generated using this example (or a close variant of it).
So far, little effort has been done to improve its performance. The focus currently is on having a clean design, and to grasp the concepts gleaned from the aforementioned book.