Is Nikon Capture NX-D free?

Yes. Capture NX-D is absolutely free.  Anyone can download it from the Nikon Download Centre. Just typing Capture NX-D into your browser should take you to the right place.  Anyone can make use of Capture NX-D  but it is particularly useful if you own a camera which can produce Nikon raw files.

Is Nikon Capture NX-D any good?

Yes. If you own a Nikon camera which produces a Nikon raw (NEF) file and you don’t already own software you have paid for ( like ph*t*sh*p), then you should certainly try Capture NX-D.  Although you can use NX-D to edit JPEG or TIFF files, it really comes into its own when you shoot in NEF format. NEF files store a considerable amount of information which is not stored when you shoot JPEG.