I wish I had an app for concerts and other music-related events. For example, according to my taste in music and where I live it would let me know when there would be a concert or event that might interest me. Of course I would also be able to manually pick bands that I like and to get a special notification for them.
There would also be other features such as rating a band or an an event that I went to. We would also be able to leave comments on there for the different artists to see.
Also, there would be chatrooms to be able to talk to other persons with common interest (in music), and sometimes maybe even be able to talk to some artist.
Im sure an app like this would be possible or even already exist. The only hard part would be to have the participation of the artist and for them to agree to sometime take the time to look at comments, or participate in the chatrooms.