Geist: The Sin Eaters is the seventh Chronicles of Darkness game to be released, and the fourth limited run series. It was first announced on August 14, 2008 in the back of the , and was released on August 13, 2009.
Unlike the other limited release lines, which had four sourcebooks in addition to the core book, Geist only had one sourcebook released, World of Darkness: Book of the Dead. There are no further plans for any more major Geist releases at this time, although minor adventures and character books have been released via .pdf.
See also: Bound
Sin-Eaters, also known as the Bound, are mortals who have died, but made deals with strange, alien spirits called Geists to return to life. This does not come without a price; they must share their body, mind, and desires with the Geist, and often spend as much time confronting the death around them as well as appeasing their new "friend" as they try to continue their own life.
See also: Geist
Geists are a special kind of spirit who are former ghosts that have separated themselves from their mortal identities, embracing the ideas and imagery of their deaths, coming to embody those images. They are capable of making special pacts with humans near death, combining with them to create the Bound.
See also: Key
When one of the Bound has their near-death experience, also called a Threshold, it also gives them an affinity with a certain Key; this Key taints the way that a Bound can use their powers. This also ties into their Keystone, a special artifact reflecting the manner of a Geist's death. 
See also: Manifestation
See also: Psyche
Because two personalities and mind are inhabiting the same body, the human Bound and the Geist must learn to work together to somehow obtain their goals, making them prone to weakness when the two halves just don't get along. Psyche describes the bond that Geists and Bound share with one another; the stronger a character's Psyche, the more will each half of the Bound is willing to contribute to a goal.
See also: Krewe
A Krewe is a term for an alliance of Sin-Eaters. They scale from small, localized groups akin to street gangs to grander occult-based organizations akin to the secret societies that Sin-Eaters gathered into originally.