Nobilis is a roleplaying game written by authoress Rebecca Borgstrom (the cover credits "R. Sean Borgstrom", supposedly because the author feared that RPG players would be prejudiced against an RPG written by a woman).
It has been published three times: the first edition in a salmon-coloured trade-size hardback by Pharos Press, and the second edition in a white-coloured art-book sized hardback with an attached marker ribbon by Hogshead Publishing, and then later by Guardians of Order (the colour of the marker ribbon varies between the printings).
The game's theme is that the godlike figures who created the Earth, and other worlds ("Imperators") have been forced to leave in order to fight against invading forces aiming to destroy everything ("Excrucians"). In their stead, they appoint humans ("Soverign Powers" - or "Nobilis") to rule over the aspects of reality they previously had control of. So a player may, for example, play the Power of Guns, the Power of Technology, or the Power of Communication.
The game is based on a diceless system with a very unusual stat block. Characters have only four basic stats: Aspect, which defines how well they can accomplish mortal tasks; Domain, which defines how much power they have over the thing they are a Power of; Realm, which defines how much power they have over their Chancel (a particular place where the Powers reside); and Spirit, which defines to what extent the Power is defended against hostile actions others. As a guideline to the power level of the game, a character with Aspect 0 is an average human in all respects; at Aspect 1, they are as good as the best in the world at everything. Starting scores for stats may range up to 5.
Because of the tremendously high power level, the difficulty of working out a logic that can be used to establish behaviour in such a highly mythical setting, and the highly florid writing used in the book (for instance, every level and every stat is described by a short fable!), Nobilis is renowned as an exceptionally difficult game to run and play; it sparked the origination of the term Borgstromancy. There are still circles in which the announcement that a player or group has successfully played or run Nobilis is still cause for gasps of admiration or even applause.
A supplement, titled A Society of Flowers, was supposedly in production for the first edition but has never been published.