You can play different songs on the piano in Tifa's room in Nibelheim.
How to play the piano
You have one octave to play with. The notes are as follows.
You can also play three different chords.
If you play all the notes in order (as in on the list that comes up, you receive tifa's secret savings, a mighty 1 gil.
Songs to try
So far, see Tifa's limit break on information on how to play the Highwind theme.