Autodesk is not keen on the Open Design Alliance and its DWGdirect libraries. (The world's largest CAD company even doesn't care for ODA using DWG in the names of its products, even though ".dwg" is merely an extension for files, like ".xls" for Excel spreadsheets.)
But here is one reason to cheer on the efforts of ODA: their DWG API supports more operating systems than does Autodesk's own API. This allows users on many more computers to access files saved in the worldwide standard for drawings:
-- Linux X86
-- IBM AIX
-- Windows CE
Oh, and also desktop Windows, bot 32- and 64-bit. Autodesk's RealDWG API runs on Windows Vista, XP, and 2000.
If you need to access DWG files on Linux, who you gonna call?