6 links
ARX LT SDK
cadaware.com
An extension to AutoCAD LT to enables the ObjectARX API as with the standard version of AutoCAD.
AutoCAD Developers Group Europe
adge.ch
A non-profit association of software developers who are working on applications around AutoCAD.
AutoCAD Exposed
manusoft.com
Information about undocumented features of AutoCAD, such as commands, system variables, and functions of the ADS, ARX, and AutoLISP programming interfaces.
OpenDWG Alliance
opendwg.org
An association of CAD customers and vendors committed to promoting Autodesk's AutoCAD DWG drawing file format as an open, industry-standard format for the exchange of CAD drawings.