Michael Winter: a tone for one or more strings [2004]
Other sources of one-note-once music
that may or may not be considered composed pieces:
William Gardiner: transcription of a struck half-crown coin, from "The Music of Nature" [1832] score
F. Schuyler Mathews: transcription of the dive of a nighthawk, from "Field Book of Wild Birds and Their Music" [1904] score
Marin Mersenne: The single permutation of 1 pitch, from "Harmonie universelle" [1626] score
A hunting horn signal to call one's companions, as described in Jacques du Fouillou's "La Venerie" [1561] score
3 more hunting horn calls, as described in L.C.R. Cameron's "The Hunting Horn" [1910] score
A single tone used to get illegal free long distance calls (a blue box), as described in 73 Magazine [June 1975] description
A fragment of Ancient Greek music that contains only one note [3rd century BC] description
Catagorized by Pöhlmann & West as Fragment 52 of entry no. 6 in their book "Documents Of Ancient Greek Music"
PAP. ASHM. INV. 89B/29-32