Nemulon-9 is the cybernetic assistant sent with Shelley Winters by the Ministry of History when she goes on missions to fix the timeline via time travel. Barbara (Babs) remarks that "no one's exploded using one of those yet" on seeing which model Shelley had just been issued, implying that predecessor devices Nemulon-8 and earlier had problems along those lines.
In its compact form, Nemulon resembles a Viking helmet, but it expands out into a roughly human-sized robot (which Shelley terms a "cybernetic demonoid... steam-punk nightmare", but later comes to appreciate after Nemulon provides assistance to her mission). It is also able to change to a variety of other shapes as well, as needed for camouflage or utility. It provides useful advice and information, though it tends to show a somewhat caustic wit.
Nemulon is also apparently capable of writing music reviews, as it provided some for the 2015 end-of-year review series.