ArcGIS for AutoCAD is an extensible and customizable add-on for AutoCAD that can be used to support CAD and GIS data creation and data maintenance workflows. You can create your own custom solutions using a combination of the API extensions to AutoCAD, external API to ArcGIS, and specific AutoLISP tools provided within the plug-in.
Esri extensions to ArcGIS for AutoCAD
The ArcGIS Indoors extension to ArcGIS for AutoCAD, called ArcGIS Indoors for AutoCAD, customizes the user interface with additional tools used in workflows for preparing CAD data for integration into ArcGIS Indoors solutions.