Drishti (from Sanskrit word for "vision" or "insight") is a multi-platform, open-source volume-exploration and presentation tool. Written for visualizing tomography data, electron-microscopy data and the like.
An R package for the (3D) visualisation and analysis of biological image data, especially tracings of single neurons. nat is the core package of a wider suite of neuroanatomy tools introduced at http://jefferislab.github.io.
vmtk is a collection of libraries and tools for 3D reconstruction, geometric analysis, mesh generation and surface data analysis for image-based modeling of blood vessels.
Facade API on top of JOGL (http://jogamp.org/jogl/www/) offering a simple interface for creating OpenGL contexts/windows, GLSL shader programs, and textures. Use it in your favourite JVM-based language.