Multi-Dimensional Transfer Functions for Volume Rendering
Simian is a volume rendering tool for scientific visualization and medical imaging. It is being developed at the University of Utah in collaboration with the Advanced Computing Laboratory at LANL, and is the product of research being conducted by Joe Kniss, Gordon Kindlmann, and Chuck Hansen.
It features: Multi-dimensional transfer functions Direct Manipulation Widgets Dual-domain interaction Shaded volumes
http://www.cs.utah.edu/~jmk/simian/manual.htm