Dalek harvest ships were flying saucers utilised by the Daleks. The Twelfth Doctor referred to harvest ships as ancient technology, almost "first generation" by Dalek standards, and that they must've taken the ships "out of mothballs" for the Last Great Time War. Because they were was so old, the ships did not respond to Dalek orders but rather Dalek "base code," i.e. Kaled commands.
The harvest ships were used to harvest children from planets. Children would have their brain's hooked up to battle computers; having previously robotized them completely, now they were used to augment the pathweb. (COMIC: Harvest of the Daleks) The Daleks also used harvest ships to capture populations to turn them into cyborgs.
A fleet of harvester ships descended on Carter Baross which the Time Lords destroyed by bombarding the planet. The War Doctor subsequently followed a distress call belonging to a damaged harvester disguised as a salvage ship en route to Tharius, pretending to fall for the trap so he could use a cyborg he'd saved from Carter Baross to compromise it. The Supreme Dalek aboard attempted to foil his plan to use the self-destruct by increasing the storm drive so its detonation would also destroy an entire solar system. The Doctor responded by triggering his Battle TARDIS' detonation to destroy the storm drive and deactivated the self destruct, leaving the ship on a catastrophic collision course with Tharius whilst he escaped with using the ship's time drive in hopes of evacuating the population first. (AUDIO: Saviour) He used an Artron generator to halt the ship as it fell towards Tharius, (AUDIO: Consequences) but with more Daleks on the way to harvest the population he was eventually forced to concede defeat and let the harvester fall, destroying Tharius. (AUDIO: Destroyer)
A harvester was frozen in time by the Time Lords and placed on Memnos. The War Doctor brought Case to it in hopes of using her to awaken the nascent cyborgs aboard without Dalek conditioning, however she was furious at the idea. He ultimately agreed and destroyed the ship. (AUDIO: Memnos)
Long after the Time War, the Twelfth Doctor and Bill Potts discovered an automated harvest ship abducting children on Gosligi's Branch. The Doctor put it in a holding pattern, stripping its software to its most basic levels, and gifted the ship to the people of the planet. (COMIC: Harvest of the Daleks)