Fomus

(fomus
 :output '(:lilypond :view t)
 :parts (list
     (make-part
      :partid :flute
      :name "Flute"
      :instr :flute
      :events (loop for o from 0 to 20 by 1/2
            collect (make-note :off o :dur 1/2 :note 72)))
     (make-part
      :partid :tuba
      :name "Tuba"
      :instr :tuba
      :events (loop for o from 0 to 20 by 1/2
            collect (make-note :off o :dur 1/2 :note 48))))
 :events (loop repeat 10
           collect (make-mark :partid (case (random 2) (0 :flute) (1 :tuba))
                  :off (random 20.0)
                  :marks '(:accent))))