I searched long and hard, hi and low for a free or open-sourced cad several years ago, and I stumbled finally upon this by the makers of SolidWorks:
http://www.3ds.com/products-services...-cad-software/
Totally free, and supported as well. You can also find you-tube content and forums to help you. For those desiring a more robust 2D cad, you can buy the pro version. I find the free version does all I want from a 2D cad.
For those familiar with older AutoCad 2D products, the interface will be surprisingly familiar.