dxf

LibreCAD is a cross-platform 2D CAD program written in C++11 using the Qt framework. It can read DXF and DWG files and can write DXF, PDF and SVG files. The user interface is highly customizable, and has dozens of translations.

F3D is a fast and minimalist 3D viewer desktop application

A free viewer for DXF files.

MeshCAM is the fastest way to generate G-code