MatterControl - MatterControl is a free, open source app that lets you organize and manage your 3D prints.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Slic3r - STL-to-GCODE translator for RepRap printers Here comes Slic3r! Its features are: - speed
Autodesk AutoCAD - Autodesk AutoCAD is a commercial computer-aided design (CAD) and drafting software application.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
FreeCAD - An open-source parametric 3D modeler