The Boomerang Dagger (Boomerang Dagger +2 in-game) is an enchanted dagger +2 which can be used in melee combat or be thrown, and as the name says, it will return to the owner. This dagger has the same bonus to damage and THAC0 as a dagger +2, but a speed factor of 1 instead of 0. This item appears in Baldur's Gate II: Shadows of Amn. It can be obtained if the group of mercenaries in Delosar's Inn at the Bridge District is killed.
Fullen Woolspinner, an ambitious halfling from a well to do family, left his home to spend several years adventuring. During his travels he ended up staying with a family of dwarven weaponsmiths. Much impressed by their throwing axes, which always returned to the hands of their wielder, Fullen sought to make a dagger that could do the same. With the help of his dwarven friends he succeeded, creating several of the famous Fullen Boomerang daggers.