Ball of Pet Summoning
Balls of Pet Summoning are dropped as uncommon loot by Solen Queens. Once "linked" to a pet, they can be used to summon that creature to the owner's location - even if the pet is stored in the Stable. Although they retain their "linked" status when passed to another character, only the pet's actual owner may use the ball for summoning purposes - A different character may only remove the link and then create a new one with a pet of their own.
The balls must be recharged on occasion using Translocation Powder. They may hold 30 charges at their maximum. Not sure if they become "saturated" like Bags of Sending, never actually used them myself.
Many tamers make use of a different trick in order to "summon" their pets to difficult areas: Logging out and then back in will drag an unstabled pet from anywhere in the game world to the owner's location (so long as the owner is not dead).