Ubuntu Guide posted a quick tutorial about installing gCAD3D in Ubuntu

gCAD3D is a 3D CAD CAM application that features an integrated 3D OpenGL viewer, a program interpreter for geometry and NC-commands in 3D, an integrated NC-processor, and a programming interface for user programs. It has support for importing Step files and support for both importing and exporting Iges, DXF, and VRML files.

  Install gCAD3D, the Open-Source 3D CAD CAM Application in Ubuntu