Finale is also a
sheet music composer that allows for just about anything. It has excellent
music output and could help a person
play an instrument better. Just write in the music and tell it to play it with your instrument and
voila, your music is played back to you.
The interface takes some getting use to and not all of the features are obvious right away, but its a damn good grab. Of course if you are a
cheapskate and don't want the full abilities of Finale, they have
Finale Allegro which is a watered down version.