gCAD3D is a powerful 3D CAD-CAM application, that features built-in integrated 3D OpenGL viewer, NC-processor, program interpreter for 3D geometry, etc, features backed by a solid import/export approach (supporting Step, Iges, VRML, DXF, SVG, etc).
gCAD3D has been updated to another interesting release, 1.91, introducing support for GTK+3.