This game is stuck in the development limbo known as Vaporware. Few to no details have been released about its gameplay, plot, or release date since its announcement many years ago. It may or may not be in active development, but neither has it been cancelled officially.
Skull & Bones takes place in the Indian Ocean, and in it you'll be able to play with friends, fighting of AI pirate hunters, and against friends, in 5v5 player versus player combat across a variety of modes. You'll choose from a selection of ships and customise them, from a small sloop up to a giant frigate.