I would like to copy my finished films as well as my source material to several drives for back up reasons, obviously ...
But I would like to know if anyone knows an application that will let me set this up easily, so I can do it in one go.
In other words, I would like to drop the file on an application or application droplet, which then takes care of copying the file to pre-selected drives (folders).
macOS's "Folder Actions" may be able to do this. But a more standard solution is to get a quality backup application such as Carbon Copy Cloner and set it to backup your drive automatically as a pre-scheduled time. CCC can do incremental backups, so that after the initial back-up, the rest will only move files that have changed since the last back-up, or are new since the last back-up.