The Hunter Ranger’s Horde Breaker feature states:
Once on each of your turns when you make a weapon attack, you can make another attack with the same weapon against a different creature that is within 5 feet of the original target and within range of your weapon.
We also know that unarmed strikes count as weapon attacks and in particular the Sage Advice Compendium states:
For example, an unarmed strike counts as a melee weapon attack, even though the attacker’s body isn’t considered a weapon.
However, the Horde Breaker feature states that you must make another attack within range of your weapon and unarmed strikes are not weapons. So can you use an unarmed strike with Horde Breaker?