I need to give my "Gothic Pipes" CD another play. It has the earliest known organ music they could find, dating it looks like as far back as 1359. There's some secular dances and songs (my favorite title translates to: "Get up, you sleep too much"
) , and two Kyries and a Gloria. Those are done antiphonally, so the famous Capella Romana choir sings a line, the organ plays something so the next line is missing, etc.