Hydrate, by Planet Waves, is my new favorite fingerboard conditioner for rosewood and ebony fingerboards. For 36 years, I have only used boiled linseed oil. I have been using Hydrate for 6 months now and like it so much, I have added it to my store! Just spray a little on a small piece of soft paper towel, coat the entire fingerboard (strings removed, of course), and then wipe off the excess.
For maple boards, I suggest you use our Everyday Polish.