Artifact wooden flute that makes humanoid monsters within range begin doing a multi-step dance when they hear it; they can’t escape from the dancing until it finishes, they are unable to take their next step (bad terrain, a trap they know about, etc) or they are hit by something.

Improvising on a wooden flute may compel all r monsters (or just the rats) within its audible range (or the whole level) to move closer to you or follow you, a reference to the Pied Piper of Hamelin.

Playing a wooden harp (and possibly a wooden flute) near intelligent peacefuls may cause them to give you some money or items from their inventory, but there’s also a chance that they become hostile (without an alignment penalty though).

Soldiers occasionally drop piccolos, which act similarly to wooden flutes (but made of metal).

This could also be done in the object materials patch without adding a new item for piccolos, by simply having them drop metal flutes.