The DWG format is used mainly by CAD (Computer-Aided Design) applications for saving and storing 2D and 3D design data and metadata.
Because it is the most widely used format when dealing with CAD drawings, this file format can only be opened and edited using a wide range of 3rd party applications.
DWG viewer apps allow users to view their files' contents without needing AutoCAD or another dedicated CAD application installed on their Mac.
Some DWG viewers also enable theikr users to convert their DWG files to other file formats that can be processed easier.