gCAD3D is a 3D CAD-CAM application which features an integrated 3D OpenGL viewer, a program interpreter for geometry and NC-commands in 3D, 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.
OCE (OpenCascade Community Edition) is a community version of the OpenCascade Technology 3D kernel, a C++ library for 3D CAD development. It includes components for 3D surface and solid BRep modeling, visualization, data exchange (STEP, IGES), and rapid application development. OCE aims to fix bugs and improve code quality and portability.