Popup menu items in Element Settings
If an Add-On can add custom data to elements to be listed by its own listing engine, then it will be listed in the Listing Attributes tab page in ALL Element Settings dialog boxes, including even lines, hotspots etc.
Popup menu items in Open/Save dialog boxes
I/O Add-Ons can add file formats to these directory dialog boxes.
Add-Ons can use the standard Archicad process indicator with their own custom messages.