I decided to stop update of xPiano.
It will continue to be on the Android Market, but there will be no update in the future.
I explain the reason in the page that the following link represents, but in short, updating xPiano became a burden for me, rather than informative experience.
I really appreciate all your suggestions you gave me to improve this application and encouraging comments. I continue to update xPiano+ and develop other Android applications.
Thank you for all.
About xPiano update Stop