The AutoCAD 2014 ObjectARX SDK is now available for download from the "Autodesk Developer Network “ADN” web site. Many of the 2014 products in multiple languages are also available for download by ADN members.
The 2014 ObjectARX SDK will also soon be available to everyone at http://www.autodesk.com/objectARX but currently there is a web page issue being looked into.
“The ObjectARX® programming environment provides object-oriented C++, C#, and VB .NET application programming interfaces for developers to use, customize, and extend AutoCAD® software and AutoCAD-based products, such as AutoCAD® Architecture, AutoCAD® Mechanical, and AutoCAD® Civil 3D® software. A version of ObjectARX for AutoCAD® for Mac® software is also available, though not all APIs are available in the Mac version.
ObjectARX programming environment libraries provide versatile sets of tools with which AutoCAD API developers can take advantage of the open architecture of AutoCAD software. They also provide direct access to the AutoCAD database structures, graphics system, and native command definition.“