Currently looking for a manual camera app for my new 7+. It doesn't have to be free.
You didn't specified what features do you need

Do you need recording video? capture RAW? bracketing/burst? There is a list of apps that do this (ordered by price):
- Camera++: photo, video, burst, bracketing, slow motion, time lapse, RAW - 2.99$ (my app)
- Manual: photo, RAW - 3.99$
- ProCam: photo, video, slow motion, time lapse, editing, long exposure - 4.99$ + IAP
- ProCamera: photo, video, slow motion, time lapse, long exposure, editing - 4.99$ + IAP
and few more