IExternalApplication vs IExternalCommand

Besides IExternalApplication there is another add-in interface which can be implemented called IExternalCommand. External commands are “light” versions of external applications in a way that they usually represent smaller, short-lived actions (commands) which may not even have a dedicated user interface dialog. No dedicated ribbon space needs to be configured for commands, instead, they are automatically placed inside the external commands list in the default “Add-Ins” tab (see figure below). In .bxa file add-in type “Command” must be specified instead of “Application” in order to be registered by the host app.