The Mind-wiper was a memory-erasing device created by the Head Alien in It's Walky! to prevent abductee children from remembering the procedures that were performed on them. Following Head Alien's capture, the device ended up in the hands of SEMME.
The Mind-wiper could be used to remove selected portions of the target's memory, but each subsequent mind-wipe was less effective than the one that preceded it. Repeated mind-wiping could have detrimental effects on a subject, and past a certain point, the procedure stopped working entirely - something Penny found out at her own expense when she attempted to wipe David Walkerton, the abductee whose memories had arguably been most tampered with.
The JFO's Britjas apparently carried ranged mind-wiper weapons as standard issue.