LibreCAD is a completely free 2D CAD application that works with DXF (drawing exchange format) files created by AutoCAD or other similar programs. Is one of Autocad alternatives for Mac, together with DraftSight (supports DWG format), but also works on Windows and Linux.
Was released for the first time in 2011 and is available for all major platforms. It has a very intuitive and friendly interface, translated in more that 20 foreign languages, and provides different types of tools to create your layouts and objects.
Supports grids, change draw order, zoom in or out, draw different types of shapes categorized in line, arc, circle, ellipse, polyline, add text and insert images. Set dimension to whatever you want: linear, radial, angular, horizontal etc.
Work with layers, easily add or remove blocks, scale, rotate, round, view attributes and many other built in functions are available.
Although does not work with DWG files (which are more popular), you can save DWG files to DXF format because this application supports it and can be a reliable free replacement for AutoCAD or other similar programs.