Visualization Library has just released v3.2.440 Alpha, focusing on new Volume Rendering features:

This new release concentrates on volume rendering: the new vlVolume::SlicedVolume class can be used to directly render 3D volumes with and without OpenGL Shading Language. You can install your own shaders or use the default ones which support realtime dynamic Blinn-Phong lighting and custom transfer functions.

Also, they’ve improved some basic algorithms like Marching Cubes and added DICOM support.

via Visualization Library | A lightweight C++ OpenGL middleware for 2D/3D graphics.