Linken's Boomerang is an uncommon trinket especially valuable to paladins, shamans and druids, as it allows them to have a physical ranged attack.
This item is a quest reward from [56G] It's Dangerous to Go Alone.
This item has a range of 8 - 30 yards. The disarm and stun rates appear to be 3% or below.
The stun proc is a reference to the fact that the Boomerang from the Legend of Zelda series was almost always used to stun enemies.
"Linken" is a parody of Link, from the Legend of Zelda series, as the boomerang from the Legend of Zelda series can loop around and kill minor creatures, and stun higher ones.