FreeCAD - An open-source parametric 3D modeler
Slic3r - STL-to-GCODE translator for RepRap printers Here comes Slic3r! Its features are: - speed
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.
Repetier - Software for controlling RepRap style 3D-printer like Mendel, Darwin or Prusa mendel.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
MatterControl - MatterControl is a free, open source app that lets you organize and manage your 3D prints.