AutoCAD supports a number of application programming interfaces (APIs) for customization and automation. Third party software has become an important addition to the AutoCad marketplace. In recent years, Autodesk has engaged in some company acquisitions to provide some AutoCad oriented third party applications of its own, and also to expand into other design related software niches.
AutoCAD's native file format, AutoCAD DWG, and to a lesser extent, its interchange file format, DXF, have become de facto standards for interchange of 2D CAD data. In 2006, Autodesk estimated the number of active DWG files to be in excess of one billion.
AutoCAD currently runs exclusively on Microsoft desktop operating systems. Versions for Unix and Apple Macintosh were released in the 1980s, but these met with limited market acceptance and were later dropped.
