A username and password are required.
Nikon provides Capture NX-D to view, edit, and convert NEF (Nikon Electronic Format) files to other formats. It is available from http://downloadcenter.nikonimglib.com/en/products/162/Capture_NX-D.html. Alternatively, for advanced users, Nikon provides an NEF Codec at http://downloadcenter.nikonimglib.com/en/products/170/NEF_Codec.html.