VTK - the Visualization Toolkit is an object oriented, high
level library that allows one to easily write programs in C++, Tcl,
Python and Java that do 3D visualization. 

        VTK enables users to concentrate on their work by providing a
large number of excellent and feature packed high level functions that
do visualization.  The library needs OpenGL to render the graphics and
for FreeBSD machines Mesa is necessary. 

The terms/copyright can be read in the docs dir/README.html. The patented 
classes (few in number) are not to be used in commercial application 
without a license from the patent/copyright holder (listed in the class
header). Patented classes are listed in README.patented-classes.

WWW: http://www.vtk.org