ProShot (free) has been a big hit on Windows Phones, but was missing from the App Store. It's no longer absent from the iOS world, and it launches with a barrel of useful features that give your iPhone capabilities similar to a serious DSLR.
Standouts are things like auto and manual ISO settings, burst mode, timers, time-lapse with fully manual control, fingertip control of ISO, shutter speed and white balance, manual focus assist and custom modes so you don't have to stick with just auto, program and manual modes.
The app supports EXIF metadata, an internal camera roll, and a grid overlay that can be customized by color. Shutter speeds can be up to 8 seconds, perfect for night photography.
The iOS incarnation of ProShot did not carry over all the features from the Windows Phone version, but most are coming, including the ability to shoot video. The app doesn't do any editing or processing at all. Take your picture with ProShot, and make your adjustments in another app.