In ArcGIS Online, you can create an attached table. You can add columns to this table and update the entries in the table however you cannot add a row to the table. The map can be opened in Collector and then another row can be added to the attached table. There is currently no way to create another row in ArcGIS Online for an attached table.
Field staff use Collector to record data. Occasionally management needs to add data to an attached table. In order to do this, management, who are already on ArcGIS Online, need to use a mobile device and the Collector app to add another row. Having some functionality in the table (ideally) or in the popup that would allow users in ArcGIS Online to add rows to attached tables would be great.