I've always liked making up theories about a common cosmology. Werewolf is my favourite OWoD game, so that's my starting point, coupled with Revelations of the Dark Mother. I think Vampire and Demon fit in quite well, while for Mage I have a couple of ideas (what are really avatars) but nothing conclusive since I don't know the game really well.
If you're interested and can bear my english, I'd gladly share my personal theory (which is really particular and I already know that not everyone will like it) with the forum.
----
Foreword:
You should remember that I consciously decided to use Werewolf as a starting ground. I'm sure Demon is a good starting ground, as is Mage, but this is not the case.
This is not supposed to be THE TRUTH about WoD. I only found a way to make things work, discarding (or disregarding) as few inconsistencies as possible.
To understand this theory, you should be familiar with:
Werewolf
A bit of Demon
Revelations of the Dark Mother, RotDM for short
A Planescape book that explains the Modrons, or, if that's not possible, the TCP/IP protocol. (Weird, isn't it? Stay tuned!)
Fundamentals.
First of all, we should understand what was there at the beginning.
In the beginning there was chaos, where material reality and spirit were united, and also concepts and so on. I think both Axis Mundi and Demon are a good way to understand this state. This primordial Chaos we wil call Gaia, as Gaia for this theory is matter in a pantheistic way.
en.wikipedia.org/wiki/Pantheism
Anyway remember that Gaia strives to reach balance.
It's not clear if Gaia was or is sentient, so we don't know if Gaia used the Wyld to start making life out of this chaos, or if the Wyld acted on its own initiative. Then came the Weaver, that saw that every life could grow to meet its true potential. And then the Wyrm, that took those that reached that potential, their duty, and brought them back to the primodial chaos, so that the Wyld coul use their 'stuff' to give birth to something else.
Things were perfect back then, as the Wyrm did not "kill" anything, the beings themselves were eager for its embrace once they reached their potential and fulfilled their duties.
Up to this point this is canon werewolf, but RotDM is going to kick in soon.
Soon, the Weaver understood that the Wyrm was gonna grasp everything that existed, sooner or later, so if the Weaver fulfilled its duty, or if the Wyrm so chose, the latter would take the first. The Weaver was afraid of dying, so he concocted a plan. In Werewolf, we see the Weaver trapping the Wyrm in her webs. This means that while before this, the Wyrm chose who to 'kill', now the Weaver was directing its course. So instead of taking the ones that fullfilled their roles, the Wyrm had to follow rules. If you bleed too much, you die. If your heart stops, you die. We can't really know what exact rules the Weaver estabilished, beacuse spirit and matter where still one.
No we jump to RotDM. In that book, Jeovah tells Adam and Lilith that he created the Tree of Life. Its purpose is keeping the Ancient One from closing his eyes, because if he does, everything that exists wil disappear, and a new world will be created when he opens his eyes again.
So now what we have here is that Jeovah is the Weaver, the Ancient One is the Wyrm (since it doesn't state anywhere that the Ancient One deed indeed create anything), while the Tree of Life is the symbol of immortality for Jeovah, a symbol of the Weaver trapping the Wyrm in its webs.
Recall now that two fruits appear in the bible (and in hebraism too, I think), the Fuit of Life which God gave to the Angels and the Fruit of Knowledge that no-one should have eaten, but Adam and Eve did. As said in RotDM, Lilith ate both.
Now is probably a good time to introduce Angels.
It is said that Jovah created the world. But as the Weaver didn't create anything on her own, we can see Jeovah/Weaver as the being that took apart the spirit and the flesh. Jeovah/Weaver and her spirits (the Angels, back then) engineered the separation, 'creating' the physical world and shaping it, claiming to be their creators. You know you have all the houses from Demon, so each house had the task to oversee the separation of one aspect of creation.
In particular we have 2 houses (Devourer and Slayer are their demonic counterparts, can't remember the name of the Angelic houses) that used to channel the effect of the wyld and of the wyrm in the material world. The devourers set rules for birthing things. Coupling, genes, and so 0n (before that, in the umbra, you could never say what could be the offspring of two... beings). Same for the slayers, as I already said the weaver spirits/angels decided when a thing should be cast out of the material world into the mouth of the wyrm, instead of letting him choose for himself.
Now, since the angels did not eat the Fruit of Knowledge, they function like modrons, or like a layer of the TCP/IP stack. Remember that they are spirits of the weaver, so they only know and only see what their master wants them to. They can see what's above them, Jeovah, and what's below them, humans and the material realm, but they can't really see what's going on in the rest of the Umbra and absolutely can't see anything pertaining the other Celestines, the Wyrm and Wyld. (This is not even required for the devourers and slayers, they do what they do but they don't know where life energy comes from and goes to, outside of the material realm.)
----
So, let's streamline this a bit.
The weaver doesn't like the prospect of dying, so she concocts a plan. Her angels/spirits separate spirit and matter "creating" the world, trapping the Wyrm with the Tree of Life and disponsing rules for birth, life and death. Then she creates Adam and Lilith. Lilith disobeys and is cast out from Eden. Later she comes back, and tricks Eve in eating the Fuit of Knowledge. At this point in RotDM, Jeovah destroys the Tree of Life, saying something like "you have doomed us all, sooner or later the Ancient One will close his eyes" and this is when the many heads of the Wyrm start escaping between the strands of the web. The Gauntlet also gets WEAKER at this point.
Meanwhile (can't remember exactly when, if it's before or after she is cast out) Lilith has eaten both the Fuit of Life and the Fruit of Knowledge. This means she is the single entity most similar to Jeovah himself.
The Ananasi splatbook tells us that once the Weaver, out of fear of dying, created a back-up copy of himself, a copy that could take its place in case something happened to him. The copy was exactly like him, but could not create anything on her own.
RotDM tells us that Lilith was desperate (and angry with Jeovah, I think) because even if she had eaten both Fuits, she could not make the Trees grow herself, only Jeovah could do that.
See where I'm going? If Jeovah is the Weaver, Lilith is Ananasa. Let's not forget that Lilith is said to be mother to monters; and Ananasa, well, 'nuff said.
So Ananasa/Lilith has now passed countless ages trapped in Jeovah/Weaver's webs, where he secluded her after she tried to overthrow him.
----
A couple of passages of RotDM I've salvage by my previous post on an italian forum:
Once, all was silence and stilness. This was the Time of Nothing, when the Ancient One rested Its eyes and moved not. Every 55,555 years, the Ancient One breaks Its rest and opens Its eyes, to see what was not there before. Each 55,555 years, It closes Its eyes, and all becomes silence and stillness again. (1)
Then the Ancient One opened Its eyes for the 333rd time, and a bolt of Light spilt the darkness. (2) Thence came [Jeovah] (3) and the other Shinig Ones. (4) To delight the eyes of the Ancient One, they Spoke great Words and sang great Songs, and thence wove the world into being.
(1): This beginning is missing from the Hebrew version, but can be plainly seen in the Greek and Ba'hara editions
(2): This parallels the Kabbalistic explanation for the Creation, in which Divinity looks at Itself and splits the Nothingness with a flash of light.
(3): In brackets (parentesi quadre), I have noted the modern names of these deities, servants and children; the older, esoteric names offered in the original text would be unintelligible to the avarage reader. As the original sources of translation are lost to time, I have taken the liberty of interpreting these entities in the light of the symbols which represent them.
I've used the appellation "Jeovah" to reflect the god of the Hebrews, to which the author clarly refers; the Greek manuscript simply says Theos Kanova, an uncertain distinction given the Greeks' pantheism (but possibly based on a misapprehension of "Jeovah"). Jeovah itself is a corruption of YHVH or "Yahweh," but YHVH implies the greater entity that manifests through the several ELOHIM (often designated as angels). Still, the Hebrew text often mixes ELOHIM with YHVH ELOHIM - that is, "The Gods" with "The Lord God." Confusion? Translation error? Or some Israelite's snide comment about his people's religion? Such sentiments were not unknown in bygone ages...
To distinguish the words and actions of Jeovah from those of other characters, I've retained the Christian practice of capitalizing pronouns which refer to Him.
(4): "ELOHIM" in the Hebrew text, implying several manifestations of the greater YHVH.
----
This is after Adam and Eve get tricked and eat the Fruit:
Jeovah's wrath was as the lion upon an infant. His roar cracked the trees; His bellows shook the True Earth, spittig it asunder; the gnashing of His teeth caused the third part of the stones to shatter; His spittle was like fire, and it consumed the flowers of Eden.
And the Tree of Life withered in the wrath of Jeovah; as the man, the Woman and Lilith watched, it turned to ashes and blew away in the anger of the Lord of the Garden.
For thus the Cycle was begun again. The Wine of Immortality was spilled and the cup of it broken at the roots of Eden. And the world began again; the dream fell from the skies and was consumed by the anger of the Lord of the Garden.
And He was ever a prisoner of the Wine, and could not undo what had been done. At the closing of the Ancient One's eyes, He too would perish. Even He, the Lord of the Garden.(36)
(36): Hence the real source of Jeovah's anger, and the true achivement of Lilith: death for all, even the gods. Lilith's actions - and those of Eve and Adam, too - triggered the end of a delusion. By estabilishing a Garden and anchoring it with the Trees of Life and Knowledge, the Firstborn had hoped to stave off the closing of the Ancient One's eyes, ans thus make his world immortal. The "corruption" of those Trees by lesser creations ruined the plan and ushered in mortality. Lilith thus becomes the destroyer of this world and the sworn enemy of Jeovah, her creator - and, in contrast, a necessary part of the cosmic order that Jeovah had tried to subvert.
----
I once had a bunch of weird theories about Caine, but I kinda forgot almost all of them, so I'll just get a barebone theory here.
Let's start from the duty of the Wyrm. Before the Tree of Life, he used to decide who was able to stay and who had to go. After the creator of the Tree of Life, and even after its destruction, the Weaver/Jeovha took for himself the capacity to decide who was able to stay and who had to go.
So in both cases, we have someone deciding who dies, from the top of his throne.
But suddenly, Adam and Eve eat the Fruit of Knowledge, so they know what is good and what is evil. This gift is passed from father to son, as this is a characteristic that distinguishes humans from everything else even today.
So along comes a man, and he knows that killing is wrong. But it is not his duty to decide who stays and who goes, that's something only the Weaver/Jeovah should do. Nonetheless, he defies his rules, and commits something that was simply IMPOSSIBLE before (remember that the rules of the Weaver are those that shapre reality, they're not just moral issues). So Caine unleashes a massive, massive backlash of Paradox by willingly taking the life of his brother. Abel dies in an impossible way, not only without reaching his potential and fulfilling his duty, but also with pain and anger. This sends him straight into a never-seen-before umbral realm, making of him the first Wraith.
Meanwhile, the body of Caine is calcified by the powers of the Weaver's Paradox: his body will never change, he will never die.
I only have a couple of loose thread from this point on, but I'll do my best.
The Angels fought the Demons, the Angels won, the Demons get trapped in the Abyss. Anyway the Weaver/Jeovah is absolutely sure that his loyal Angels will not be loyal for long. So, as he his also concocting another plan to reach immortality, he disassembles the entire army of Angels. And by that, I mean that he takes them apart. The shards of the Shining Ones, as we know from Mage's base handbook, bind to the souls of humans, becoming their sleeping Avatars.
This is why no-one has ever seen angels. And no Demon is capable of finding them in modern times.
Instead, the Weaver/Jeovah created other spirit servants, spiders, much more loyal.
So why would ever W/J give the humans such power over reality? The power to use the 'debug-mode' of reality, True Magik? Since they have inherited the Fruit of Knowledge from Adam and Eve, now they also have a sleeping seed of the Fuit of Life inherited from the Angel Shard. A Mage Ascends when his seed bears fruit, and the two Fruits get in tune with each other, creating in this way a being most similar to both Lilith and Jeovah/Weaver himself.
So why all that?
I really don't know. I fear, that W/J wants the whole humanity to Ascend. I also fear that, while chronologically older, the Traditions are a mistake, a branch off of what W/J was planning when he gave his preferred children, humans, the gift of the Avatar. The original idea of the W/J was more like the Technocracy, I fear. Erasing all that is supernatural, except for what is of the Weaver.