If you are a Mac user, Graphic Converter from http://www.lemkesoft.com/ has been around and maintained for a very long time. It is inexpensive and is able to process a large number of formats, including RAW.
I tried it with some D600 NEF files and it seemed to suffer no indigestion. It has the ability to import from a USB connected camera as well as handling files already imported. At $40US from the Apple APP Store, it offers yet another inexpensive solution.