A9CAD, a 2D CAD freeware drawing application, is very similar to AutoCAD. The biggest strength of the free CAD program is that it can save and read the file in .dwg/.dxf format, so you can open a AutoCAD file directly using the CAD tool and vice versa. Please note that the free cad software is for non-commercial use only, so in case you want to use it otherwise, you have to purchase the license. You can down load A9CAD here.