I'm planning on creating a new iPhone app. Any ideas?

I wanted to create a simple app but still haven’t found what category I’d like to explore.

Do you have any suggestions on what type of app I could create? Something useful and productive for instance.

I know there are already a million apps out there, so I wanted to create a new one (different from all the others) or create a new one that hasn’t been done yet.

Feel free to suggest anything!
Every idea is welcome!