It depends on what you want the app to be able to do?
Do you want it to *play* classical music? Or do you want to be able to *learn to play* classical music.
Or do you want an online *classical music magazine* that talks about classic music but also allows you to play it.
There's an app fro a magazine called Gramaphone Magazine that's pretty good. I think it's only available for the IPad, though.