MeshCAM is a professional app that allows to generate gcode. This app works with almost every 3D CAD program by opening the two most common 3D file formats, STL and DXF. If you just want to make 2D parts without using a 3D CAD program, you can load 2D DXF files (in R12 format) and extrude them to a 3D part.
Simple, open source 3D printing program.
Renders very realistic images of 3D models and scenes.
CAD File Converter gives you access to drawings in the most common CAD formats.
CAM XML editor tool for Mac.
Compatible with DWG 2010 files.