Not perfect, but it does help – Manual Viewer 2 Review

For newer and less expensive Nikon DSLR's, the instruction booklets from this app are longer and more comprehensive than the booklets that come with the camera (i.e., the Nikon D3300). For the older cameras (D70s), the online booklet is the same as the printed booklet. Not every feature of the app is seamless, but it helps to have it available in a digital or at.
Review by FredBart on Manual Viewer 2.