FreeCAD is an open source 3D CAD program that enable users to create professional layouts and designs. Area of use is unlimited, from architectural projects until industrial machines, technologies or simple objects.
Fisrt time was released in 2002 and has started as a software for mechanical engineering. Interface is intuitive and clean, it provides many drawing tools.
Allows to create 3D or 2D drawings. Does not support DWG files, but support DXF, SVG and a few more. It supports Python scripts (if you are a programmer).