The limb actuator is a cybernetic implant granted to Conrad Kellogg by The Institute. Though its purpose is never stated in-game, it can be implied by its name that it actuates (moves via motors) the joints of its host, possibly to make one's limbs stronger and/or grant more stamina.
It can only be found on Kellogg's corpse after killing him in Fort Hagen during the quest Reunions, and cannot be pickpocketed. Also, unlike the cybernetic implants found in previous games, the player cannot have it implanted in themselves, and thus its only purpose is to provide story. It can also be sold, or placed as decoration.
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