DWG

DWG ("drawing") is a file format used for storing two and three dimensional design data and metadata. It is the native format for several CAD packages including AutoCAD, IntelliCAD (and its variants) and Caddie. In addition, DWG is supported non-natively by many other CAD applications. The .bak (drawing backup), .dws (drawing standards), .dwt (drawing template) and .sv$ (temporary automatic save) files are also DWG files.

History of the DWG format
DWG (denoted by the .dwg filename extension) was the native file format for the Interact CAD package, developed by Mike Riddle in the late 1970s, and subsequently licensed by Autodesk in 1982 as the basis for AutoCAD.

The DWG format is probably the most widely used format for CAD drawings. Autodesk estimates that in 1998 there were in excess of two billion DWG files in existence.

Free viewers
There are no open source viewers for DWG files since the licensing of the libraries needed by lx-viewer now restricts their use to members of the Open Design Alliance.

Free for unlimited time

 * Linux Drawing Viewer / Lx-Viewer only for members of the Open Design Alliance
 * Design Review 2010 (36 MB) from Autodesk can view DWG files if installed with the DWG Reader (DWG TrueView) option (153 MB total) that also includes DWG TrueConvert that can convert to AutoCAD R14, AutoCAD 2000, AutoCAD 2004, AutoCAD 2007 and AutoCAD 2010 DWG file formats. For Windows XP/Vista, also 64-bit.
 * Caddie Requires registration, the free version plots and edits but does not save.
 * eDrawings Viewer by SolidWorks, 11.8 Mb. For Windows NT/2000/XP & Mac OS X 10.4+
 * Bentley View by Bentley, 58.2 Mb. Requires registration. For Windows 98/ME/NT/2000/XP.
 * VariCAD Viewer is a CAD/CAM file viewer able to render DWG files. It is the only such application which runs on the Linux operating system.
 * Free DWG Viewer No registration required. Updates every 8 months, viewing and measurement to scale with geometry coordinate snapping.
 * ProgeCAD smart Free for non-commercial use, registration required. ProgeCAD Smart can read/edit/write DWG files. Based on IntelliCAD.