This is for D20.
There are six gods in the world. They create all things. They are always vying against each other, but are also cooperating. Over the years, they have created and destroyed many forms of life.
Each god represents a stat of a character. The gods' names share consonants with their stats. So Callisto could represent Charisma.
Male Gods represent physical (masculine) stats (Str, Dex, Con). Female goddesses represent non-physical (feminine) stats (Int, Wis, Cha). Each god has a symbol.
Str = Bear
Dex = Snake
Con = Ox
Int = Cat
Wis = Owl
Cha = Peacock
There is no birth and death. There is only creation and destruction. All characters, and intelligent things, are the result of divine creation. You are created by a god, called you Sponsor. This god is helped by an ally, called a Co-Sponsor. You gain a +2 in your sponsor's ability. You gain another +0 in your co-sponsor's ability. You gain a -2 in the final ability of the triad (physical or non-physical). Sponsors must be all-male or all-female.
You can change sponsors during your character's career. You lose your sponsor's bonus, but retain all prenalties. You gain the new sponsor's bonus, and a new penalty. (Switching sponsors alot is not a good idea.) The character is a client of a god. You are free to do what you will, but the god is your sponsor, so you would be wise to do his bidding.
Record your race as Sponsor/Co-Sponsor. For instance, Race: Int/Cha.
Each character gains a feat at first level. This feat must have a prerequisite in your sponsor's favored stat. Each character gains an extra skill point. This point must be spent in a skill based on your sponsor's favored stat.
Feats from Savage Species are open to all characters.
Gender of a character has nothing to do with masculine or feminine stats (aside from the gods that represent these stats.) However, gender does have to do with social perceptions.
Each god has a unique agenda that the created character seeks to uphold.
Strength seeks to uphold the martial prowess of a society and the people's ability struggle.
Dexterity seeks to uphold the adaptability of society, and its diversity.
Constitution seeks to uphold the institutions of society (army, government, kingship).
Intelligence seeks to uphold the learnedness of society.
Wisdom seeks to uphold the tradition of society, social order.
Charisma seeks to uphold the oratory and debate of society.
Naturally, in an RPG, we need something to fight. The various gods also create creatures to demonstrate the weaknesses of their peers. Charisma could create an enemy based on oratory, to show the weakness of Strength. The gods then rely on their creations to actually demonstrate that what they have created is vital. Think of this as debate through wargaming. The proof is demonstrated over time. However, as time advances, the innovations change the balance, and the cycle begins again.
A party represents the collective wisdom of the two Triads. As the party advances, the various gods throw threats increasingly tailored to them to test their theories. The organic way that the party develops demonstrate the importance of various traits, and optimal ways of integrating various traits.
Note that there is no evil here. All you have is the gods testing their own creations, to see if their creations remain viable and worthy. Society judges itself on how able it is to deal with these challenges.
Challenges tend to come from pairing of gods. These challenges are themed based on these gods. An umber hulk, for instance, is a pairing of strength with charisma. Some threats come from more gods. Dragons, for instance, are creations of all the gods combined.
Undead represent the attempt, by non-gods, to engage in creation. They take once-living forms and create imperfect life, or take living forms and attempt to improve them. All the gods abhor undead.
The gods are not all knowing, and things may be hidden from them. Likewise, the gods know things and can communicate warning to their favorite creations. (Hey, dude, Intelligence thinks you're stupid and is preparing a challenge against you. These things will fry your brains out!)
At level-up, the god may tweak you. You may take a decision made at an earlier level and change it. For instance, a character with 4 sp/level could redistribute 4 sp. This also includes choosing feats. Not that rechoosing a feat could break a feat chain, so be careful.
All characters have access to the equipment repository. At level-up, they may change out their equipment for their level appropriate gear. (See DMG). No more than 1/2 their wealth may be in a single item. 1/5 of wealth must be in disposable items. This exchange happens divinely, so it can happen anywhere.
Character don't get treasure. Your magic items only work for you. Disposable magic items work for whoever you give them to.
Some characters get destroyed. If the god likes you well enough, he can recreate you. You gain an XP debt of Character Level X 500. You may not advance in level before this debt is paid off. The party must wait 1 hour/character level before the character is recreated.
(OK. I've now explained randomly appearing creatures in inappropriate environments, lack of ecology, where monsters come from, statuc dungeons, equipment, what undead are, why things change and new abilities show up unexpectedly, and most importantly, why you fight.)