The Caciocavallo project is one of the projects accepted for the OpenJDK Innovators Challenge. Its aim is to improve OpenJDK's graphics stack to enable the use of external implementations of AWT/Java2D backends, to be able to leverage the existing graphics pipeline for partial reimplementations, and to generally improve the portability of the graphics stack. The original proposal can be found on the challenge discussion list.
http://kennke.org/~hg/hgwebdir.cgi/caciocavallo/ (not maintained anymore)
API documentation of relevant classes and interfaces
For convenience, a version of these projects is located on this site: http://kennke.org/~hg/packages/