It can be used to create this item:
Lunar-crested Knife
It is also possible to use it in battles at sea vs. NPC fleets (not usable in PVP) but the effect randomly strikes your opponents per use, which makes it less useful than the Amulet of the Sun which can strike ALL of them at once. The damage inflicted by AoS seems slightly higher as well.
I suppose it also makes for a semi-useful accessory with +1 to Archaeology skill which won't lose durability unless you use it in battle as an item, too. I hope that helps. Cheers, and great online voyaging to you.