CAD Tools

Rhinoceros3D – McNeel CAD environment that supports complex surfacing and with plugins can be used for controlling robots, CAM, physics modeling, etc.

Food 4 Rhino – Biggest site to find plugins to extend Rhino

Grasshopper – parametric design tools to extend Rhino

Fusion 360 – Autodesk suite of CAD/CAM tools

3D Printing and Fabrication Tools

Additive 3D Printing Guidelines – Good overview article on Core77

Slicer – Autodesk fabrication utility that enables physical creation of CAD model through various construction methods, stacked slices, interlocking slices, etc. This utility is included in Fusion 360 and as a stand-alone free utility.

CGTrader – a 3D model marketplace for computer graphics, 3D printing and virtual reality, backed by a strong professional designer community.  Free models available!