Hi 3dcnc, well OpenDWG is a library from a company called the Open Design Alliance, you can find some info about them on their web site here:
http://www.opendesign.com/

They've done a bunch of work to reverse engineer the DWG format (which Autodesk does not publicly document), and make a library that enables reading and writing to it.


> I have noticed that some CAD software develop there
> own DWG converters, Why?.

Well, I'm not really very sure that people are developing their own, since it is quite a large task to do a good job of it.

As far as I know software that deals with DWG will license either the ODA libraries, or the "RealDWG" libraries from Autodesk.


DXF is another story - DXF is documented (except for 3D solids which are encrypted) so there are a lot more self-developed DXF converters out there than DWG converters.


- Michael