Hi Bennet,

Anatomist can do volume rendering using GPU. It is an open source
visualization software from BrainVISA project working on Linux, Mac and
Windows. It has Python bindings.

To download it (Anatomist is included in BrainVISA package):
http://brainvisa.info/download.html

There is a tutorial explaining how to use some features. For volume rendering :
http://brainvisa.info/doc/anatomist/ana_training/en/html/ch06s09.html

Anatomist Python API documentation:
http://brainvisa.info/doc/pyanatomist-4.3/sphinx/index.html

To get help from developers/users :
http://brainvisa.info/forum/

Best regards,

      Yann Cointepas