FreeCAD - An open-source parametric 3D modeler
MatterControl - MatterControl is a free, open source app that lets you organize and manage your 3D prints.
SolidWorks - Dassault Systèmes SolidWorks Corp. develops and markets 3D CAD design software, analysis software, and product data management software. SolidWorks is the leading supplier of 3D CAD product design engineering software.
Slic3r - STL-to-GCODE translator for RepRap printers Here comes Slic3r! Its features are: - speed
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.