CAD tip # 8306:

For your maker activities, you can download and use e.g. the free 3D CAD modeler and fabrication tools based on Autodesk Inventor Fusion - Autodesk 123D Design and 123D Make.

"123D" is a family of free 3D solid modeling and fabrication software tools based on the same Autodesk technology used by millions of designers and engineers worldwide. Autodesk 123D is easy to use - you can design precise and makeable objects using smart tools that let you start with simple shapes and then edit them into more complex shapes. The Windows, Mac and cloud/mobile applications "123D" support many standard file formats.

You can also combine "123D Design" with "123D Catch" (Photofly/Photo Scene Editor) to make a 3D model of a real-world object from a series of photos.

For 2D CAD work you can use another Autodesk simple and free tool - the cloud version of AutoCAD - AutoCAD 360 (WS).