Using the Fate Accelerated Edition or Fate Core rules, you can create a ghost character or NPC exactly like you would create a human character.
Using Fate Core’s nameless NPCs or FAE mooks to make a ghost is trivially easy. So why does this book exist? To provide a more specialized look at how to use custom FAE approaches to capture the feel and complexity of creating many different kinds of ghosts. It also includes some already-constructed ghost specific stunts, and some ready made, straight from stories, ghost NPCs.