Fomus

(fomus
 :output '(:lilypond :view t)
 :verbose 1
 :parts
 (list
  (make-part
   :name "Piano"
   :instr :piano
   :events
   (loop for v from 1 to 2
         nconc (loop
                 for off from 0 to 10 by 1/2
                 collect (make-note :off off
                                    :dur (if (< off 10) 1/2 1)
                                    :note (+ 60 (random 25))
                                    :voice v
                                    :marks (when (= (random 3) 0)
                                             '(:startslur-))))))))