Promethean: The Created
The New World of Darkness' attempt to do something exotic, in the form of "Frankenstein's Monster: The Roleplaying Game". You are a Promethean, an incredibly rare unliving (not undead; your body isn't really alive, but you are a whole new entity, albeit of artificial origins and often made from corpses in some way) creature stumbling through the World of Darkness. In lieu of a soul, you have a storehouse of Pyros, the raw energy from which all life springs, but which isn't meant to exist in such a concentrated form. As a result, reality itself hates you - and that's not hyperbole. People hate and despise you on sight, animals flee from you, plants wither and die in your presence- even hanging around in one place too long eventually fucks it up as the land is corrupted and unbalanced by your presence.
Your goal, then, is to master the understanding of humanity. Through this, you can use spiritual alchemy to hone your Pyros, and eventually transmute it into a human soul, giving up all your mystical powers to become just an ordinary human... but at least reality no longer hates you, so, it's worth it, right?
As is usual for the NWOD, you have about five different sub-types, each connected to a different Humour (bodily fluid believed once to be responsible for measuring health) and Element. Frankensteins are associated with Choler (Yellow Bile) and Fire, Tammuz (Golems) are associated with Melancholer (Black Bile) and Earth, Galateids are associated with Blood and Air, Osirians are associated with Phlegm and Water, and Ulgans are associated with Ectoplasm and Spirit. A later splatbook introduced the Zeka, whose associated element is Radiation and whose Humour can be any of the above, mixed with more radiation.
Promethean has the dubious honor of being the NWoD's equivalent to Wraith: The Oblivion or if you're generous, Mage: The Ascension, in that it's a game where people read it, but don't play it. The setting is incredibly bleak, even if the tone the game is trying to go for is optimistic (since it is canon that you can achieve the New Dawn and become human... except if you're a Zeka, since you suffer a dose of rads equal to your Azoth [power stat] when you transform, and the bare fucking minimum Azoth you need to succeed at the New Dawn is one dot below the "instant death due to radiation" level), the rules are complex, it requires a hell of a good Storyteller to be run successfully what with the whole "the world despises you" thing, and frankly not a lot of people actually want to play a game where your goal is to go from a superpowerful monster to a squishy human. Especially when that squishy human then has to live in the fucking World of Darkness.
Promethean is also the only game that does not have an earlier version in the Old World of Darkness. Vampire, Werewolf, Mage, Changeling, Hunter, Mummy and Demon all have a version in each. Geist is more of a spiritual successor than Wraith, but they deal more or less with the same subject. Orpheus is the only unpaired in the Old World of Darkness, but it deals with the underworld and is more akin to Wraith and Mummy.