By that I mean a device whose sole function is to travel the stars and silently observe failed alien civilizations, cataloguing their failures and inevitable extinctions for posterity in some sort of macabre scrap book representing the Great Filters argument to the Fermi paradox.
For what plausible reasons would an alien intelligence, natural or artificial, build something like this? What purpose could it serve besides educating other civilizations in the most roundabout and bleakly confrontational way possible? Would such an artifact by its very nature have to be some E.T.'s idea of a joke or a spectacularly grim art project, or is there a good reason to make something like this for the benefit of whoever might find it?