Overview:

Ogles(1) and Ogles2 are two projects in the context of frame based stereotactic neurosurgery. Both projects include volume rendering and slice data visualization tools, mechanisms for trajectory planning and importing as well as creating 3D surface meshes (Open Inventor).

Both projects allow for reproducing the work-flow of stereotactic neurosurgery. Both strive to deliver an open source data model for neuroscientific data visualization and analytics.
Neither Ogles(1) nor Ogles2 are approved for clinical use.

Ogles(1)

Ogles(1) was developed from 2004 to 2008. It stands on the shoulders of Ogle, an 3D data visualization tool create by Dr. Michael J. Gourlay at Cora.

Shortcomings of Ogles(1) include negligence of spatial information from image headers, tedious image loading limited to command line arguments, a somewhat outdated user interface, and poor capabilities to store results. Development of Ogles(1) is discontinued.

Ogles2

Ogles2 was developed from 2012 to 2015. Ogles2 tries to get over the shortcomings of Ogles(1). It takes spatial information from NIfTI-1 images into account, loading of images as well as geometry data is integrated into the GUI. Saving of results is still sparse but greatly improved.
GUI was changed to Qt (4.8.x). Coin3D / Open Inventor was chosen as underlying 3d library (instead of pure OpenGL).
Furthermore Ogles2 allows for visualization of a deep brain electrode (Medtronic 3389). Drawing and manual segmentation are not yet implemented in Ogles2.
Ogles2 is under active development.