Familiars were a breed of experimental timeships in the years leading up to the War in Heaven. They came from an attempt to work towards timeships with sentience in a gradual way, first starting with a more rudimentary, animal intelligence. Unlike most timeships there was never any attempt to bond them to a pilot, however, the subjects that existed broke free, captured the scientists attached to the experiment and vanished.
Nevertheless, the experiment was considered a success, with many of the methods used for working with the familiars later being repurposed when dealing with 103-forms. (PROSE: The Book of the War)