In my campaign based on the Amber novels written by Roger Zelazny, I have been using the Amber Diceless Roleplaying System devised by Eric Wujcik. The system is built around the Amber books, and emphasises role playing as opposed to roll playing (e.g. diceless).
The universe the game lays down is as such:
(Much of this is extrapolation on my part, but since I run the game, that makes it law, baby!)
In the Beginning, there was Chaos, limitless and without stability. Formless, changing raw chaos filled all Void with structureless flux. One could visualize this in two dimensions as a great, slowly moving river, at which's banks ends everything. But, even in a slow river, eddies can occur, little pockets of stability where things don't move as much. Such it is with Chaos. Some eddies even last long enough for true structure to create itself before being obliterated and returned to formless mass. On one such eddy in Chaos, enough structure was able to build itself such that life was able to create itself within this pocket of stability. This life took many forms, and indeed, each being within the many species had to constantly be able to change form to adapt to the changes in environment that would so often take place in such a place. Eventually, before this place fell back into entropy, sentience was achived by some of the creatures that dwelled there. Moreover, they became able to influence the Chaos about them.
Things get a little muddled here, but somehow they were able to create a structure called the Logrus, a three dimensional shifting maze-like edifice which they could traverse. If one survived the 'walking' of the Logrus, that being became able to mold the stuff of Chaos about them. Soon, the beings had created palaces, cities, and dwellings out of Chaos, and they named these the Courts of Chaos, and themselves they dubbed the Lords Over Chaos, or Lords of Chaos. Like themsleves, their Courts would constantly shift with the slow changes of Chaos itself, but the Lords were able to sustain their structure against the entropic forces of the Chaos all around them.
And there's was a rich place, for it is said that even if one survives the traversement of the Logrus, one necessarily goes insane walking it, at least for a time. All of the non- and semi-sentient creatures that evolved with the Lord were called demons, and took many forms, like the Lords themselves. The Lords were immortal and developed powers of sorcery and conjuration to fight petty battles against one another. And they worshiped the great Serpent of Chaos, an ideological or physical manifestation of the Chaos all around them.
It is said that eventually one visionary rose among the eldest Lords of Chaos. His name was Dworkin. With the power of a Jewel that is said to be an eye of the Serpent itself, he forged his way alone far out into Chaos, and created a new structure to rival the Logrus. He called it the Pattern, and it was similar to the Logrus, but two dimensional and unmoving. Around the Pattern he created Amber, his great City to rival the Courts of Chaos, and all around Amber he used the power of his Pattern to create true, unmoving stability.
But something resonated between the two great poles of power, between the Pattern and Logrus, and between them an infinite number of refractions, or shadows of Amber came into being. Indeed, it is said that each separate shadow (if any can truly be considered separate from the others) is a whole universe, in some ways like and in others dislike Amber, and the Courts. It is also said that any universe one could imagine can be found, somewhere, out in the shadows.
And those who had walked the Logrus (or, later, those who had walked the Pattern) found that they had some control over shadow, that they could move among them and control what was in them. Our own Earth is one of these shadows.
And in Amber, Dworkin fathered a son, Oberon, to rule in Amber. And over eons, Oberon fathered many children (though, considering the amount of time, clearly showed a low reproductability rate). These children were powerful, and helped forge pathways out into nearby shadows to Amber to establish trade routes with other kingdoms.
And anyone descended from Dworkin could traverse the Pattern, and gain power over shadow. Despite the fact that all of Oberon's children (now known as the elders) seem to have done it, they still bickered greatly between themselves. Only a few years ago, when Oberon had been missing for centuries, they broke into full blown war among each other for Kingship of Amber, eventually involving the Courts of Chaos in their struggles, and nearly destroying the universe as their grandfather had created it.
Now, you will play the descendent of one of those elders. You will created a character which you, the player will control. You will decide on his/her gender, physical description, personality, age, everything. Together, you and I will create that character's background, decide who their parent is, and what they know of Amber and the Courts. The other players will likely play cousins to yours, but beware: there is little of familial love between you. Many elders actively hate each other and continue to plot against one another. Among your cousins, you are likely to have good friends and dire enemies, but trust no one! In your immortal, powerful life, you are likely to be at odds with all of them at different times. They will might have the powers of sorcery, shapeshifting, Pattern, conjuration, or Trump Artistry against you. But you, too may learn these powers to use against them as well. Or along with them, as the case may be.
Trump artistry allows you to draw Trump Cards. Trumps can be drawn of people or places. With a card of someone, you may mentally contact them if they so wish, and you can transport yourselves physically between the two places the two people are. Likewise with Trumps of places. They are very powerful creations.
Along with powers, you will have abilites to bring to bear for or against your brethern. All Amberites are very good with weapons of many kinds, but having an edge over your cousins will put you out on top. Amberites can also engage in mental battles, and the same ability which governs how good you are at using various powers you might have (you psyche) also governs how good you are at those. Physical strength is crucial when a hand to hand fight occurs, such as wrestling each other, or boxing. It also adds an edge to a melee with weapons if you are stronger than your foe. Endurance also plays a key role in any protracted battle.
The first thing to do is to read the first five Amber novels by Roger Zelazny, starting with Nine Prince in Amber. Then, start creating a really nasty character!