Capture One software recently released Capture One
Express for Nikon.
Capture One has several versions:
Capture One Pro - for most brands of cameras.
Capture One for Sony - for Sony cameras only
Capture One for Fujifilm - for Fujifilm cameras only
Capture One for Nikon - for Nikon cameras only
The Sony/Fujifilm/Nikon versions are about half the price of the Pro version.
There are also
free "Express" versions for Sony, Fujifilm, and now
Nikon.
The differences between the paid version and free version are somewhat substantial but that may depend on what you need the software to do.
The big differences are that the Express version cannot be used for tethering or camera control, you get only one catalog and you must work in catalog mode, there are no layers, and a number of editing tools are missing.
Of course the free software is meant to encourage you to buy a paid version. But if you want simple (?) but still useful (?) photo editing software for your Nikon raw files, this might be worth a try.
Nikon Capture NX-D is also free.