A flute
Flutes are small wind instruments, often made out of metal or wood.
Jenna D'Sora of the USS Enterprise-D played the flute. (TNG: "In Theory")
Captain Jean Luc Picard played the Ressikan flute. (TNG: "The Inner Light")
When Miles O'Brien was having troubles with a Cardassian vole infestation on Deep Space 9, Doctor Julian Bashir gave him a small metal flute in a box and left a note, stating "It worked in Hamlin". (DS9: "Playing God")