Company Autodesk developed many more file format for their AutoCAD application. For example DXF, whole name is Drawing Exchange Format. Basic principle of this format is using of vector graphics, which is connected with 2D graphics used for creating drawings. Its main task is allowing communication and data exchange between various applications and AutoCAD.
This file format can be used in many programs, for example OpenOffice.org Draw or CorelPaint. Like DWG this format was created in December, 1982 for MS-DOS simultaneously with first version of AutoCAD and since that it was updated many times with almost every new developed version of AutoCAD.
To open these file types, you just need to use application named Autodesk DWG TrueView.