Today, our question-askers don't want much, do they? Today's question is a whole bucket of culture and religion and thicketed questions about cultural assimilation and borrowing. Can you guys tell us about the Etruscans and their beliefs, as they are the predecessors to the Romans and set up a complex system of divinations? What can you guys tell us about them for them to be totally unique from their assimilators?
Describing what makes an entire culture unique would... well, it would require describing an entire culture, which is something scholars spend their entire lives trying to do without managing to get all the way through the possibilities. We are just a humble mythology and game blog, so we'll mostly look at the religion and myths instead, and leave the historiography to others!
The Etruscans were the people of ancient Etruria, a civilization in central Italy (around where Tuscany is now, which incidentally is named from the same root) that existed for about three centuries starting around 800 B.C.E., and which was eventually succeeded by the Roman Empire, which took over its territories along with most of the rest of the known world. There are positive miles of speculation from scholars about whether the Greeks were the major inspiration for the Roman religion or whether it was really the Etruscans they borrowed from the most, but regardless of how much influence you think the Etruscans had over ancient Italy, they definitely had some.
Most of our recorded information about Etruscan mythology comes from archaeology and artifacts; they didn't write a whole lot down, although of course they did have the ability to write, and subsequent Roman influence made it difficult to tell what was originally theirs and what was a later development. Most Etruscan mythology is preserved, interestingly enough, on mirrors - there are a ton of lovingly-preserved mirrors depicting mythological scenes, often with helpful labels to tell us which deities are involved, and studying them has been the life's work of more than one determined Italianate scholar.
This particular mirror is depicting the Judgment of Paris, a Greek myth borrowed and repurposed here, complete with goddesses looking for their ego fix and one dude with a great deal of pressure on his decision. It's very common for Etruscan mythology to borrow from the Greeks; like the later Romans, they were heavily influenced by their eastern neighbors, who were already very powerful and widely-traveled by the time Etruria became a power, so they often borrowed Greek deities to add to their own roster of gods, or grafted Greek myths onto gods they already had.
But hey, who are those gods? The Etruscans in fact had a very colorful pantheon of deities of their own, many of which don't turn back up in later Roman mythology or among the Greeks, or who do so only as sideways influences on it. The leader of the Etruscan pantheon is Tinia, a thunder god who many people think is just a carbon copy of Zeus/Jupiter, but those people are wrong. Sure, he's a great sky-father god with lightning bolts, but that's where the similarities end. For one thing, he's also a god of boundaries, particularly in agriculture (i.e., separating fields from one another and preventing trespassers), something Zeus leaves on Demeter's shoulders. More interestingly, however, he actually has three distinct thunderbolts. The first one is the "benevolent" thunderbolt, which warns mortals and dispenses wisdom but doesn't actually hurt anyone; he can throw this whenever he likes. The second one is the "half-benevolent" thunderbot, which causes destruction and warning in equal measure; he can throw it, but first he has to get the consent of a committee of gods called the Dii Consenti (basically, the rest of his pantheon). The final thunderbolt is the malevolent one, capable of destroying en masse, and he can only throw it with consent of the Dii Involuti, the Shrouded Gods. Who are they? Nobody knows. They're shrouded. The point is, Tinia is cooler than you.
Then there's Uni, wife of Tinia and queen of the gods. In the same way, Uni can't just be relegated to being a copy of Hera/Juno without losing out on a whole bunch of her essence. For one thing, she's almost always shown as young, sexy, and alluring, more akin to Greek representations of Aphrodite than Hera; and she's no jealous wife to boot, even helping midwife Tinia's infrequently-born other children. I say infrequent because, unlike the famously randy Zeus, Tinia really doesn't stray all that often, and depictions of him with lovers other than Uni are far fewer than his Greek counterpart's chronicled conquests. Even more interesting, Uni doesn't sit calmly on the bench with Tinia the way Hera tends to do with Zeus; there's even a record of her kitting up in armor and going out to fight Hercle (Herakles, in a much more hilarious-to-say form), warring until they both get tired and decide to shake hands and make up. Most unexpected of all is the end of that myth, in which Uni formally adopts Hercle, welcoming him to the community of the gods, via a ritual wherein she nurses the adult man from her breasts.
Like Aphrodite, Turan is the goddess of love and sexytimes, but that's about where the similarities end. She frequently turns up with swan wings and has a giant swan familiar called Tusna, but, more noticeably, every appearance has about a fifty-percent chance to show her as either a man or a woman (or, in some memorable engravings, both at once). She's a gender-fluid being, which makes sense for a goddess dedicated to all love, pleasure, and sex without discrimination. She's also, interestingly enough, not a famous philanderer the way Aphrodite is - she isn't married to anybody and has no steady lovers except for Atunas (the Etruscan Adonis, who is usually shown as a young boy in her care), instead wandering her sexy way around as she chooses. (Turan is not the only deity that appears mutable in form, either - she may do it the most, but many of the other gods appear with different sets of genitalia or different gender signifiers, apparently without batting an eye. Scholars aren't sure if there was a secret and complex background explaining the meaning of various gender presentations of different gods, or if the Etruscans just weren't super bothered about making a god's gender a fixed thing.)
Menrva obviously lent her name to the later Roman Minerva, but she's not a simple copy of either her or Athena. Not only is Menrva a sky goddess, able to hurl lightning bolts just like dear old daddy Tinia (she does not, one assumes, have access to the thunderbolt of doom that requires escalated approval), but she often shows up with wings, and doesn't seem to be viewed as a virgin goddess, often shown suckling children or flirting it up. Of course, she's still a war goddess and is usually shown in her trademark helmet, but pigeonhole her at your peril.
Then there's our personal favorite, Fufluns, because he is the god with the name that is possibly the most fun thing ever to say. He's the second most important god in the pantheon, second only to Tinia, which already makes him somewhat different from his counterpart (Dionysos/Bacchus), but the fun doesn't stop there; his cult, focused on revelry and violence, was so rowdy that Rome finally outlawed worship of him entirely in 186 B.C.E. He was also a prophet, similar to Dionysos and his winter oracle at Delphi, and most interestingly of all is often shown with two different women who are apparently his lovers or in whom he has an interest. One is Vesuna, who is possibly a Maenad or a goddess consort, possibly related to Cybele; the other is Semla, who is actually his mom (you can see the similarity to the Greek name Semele). This fact does not seem to discourage him in any way from being very obviously banging her in some carven scenes, which she also seems perfectly sanguine about. Oedipus has nothing on this guy.
Those are the gods with the most "major" roles, which is why they are also the ones with the most Greek influence laid over their original personalities, but there are plenty of purely Etruscan gods, too. Usil is half the reason the Etruscans don't need to use Apollo for anything, since they already had a sun god - he's often shown juggling balls of fire, which is cool, and with a very bright and shiny halo of light around his head. Suri's the other half, as a prophet-god, and dispensed his wisdom of leaf-shaped pieces of metal. Aplu, imported but unnecessary, gets relegated to the position of Medic of the Gods. Thufltha is the god of luck, favor, fortune and good will - if he's happy with you, things go well, and he's called the "bird-catcher", because he's so lucky that birds just flutter into his hands without him having to put forth any effort. Tiv, Laran, Thesan, Nethuns, Culva - there are tons more, some with fascinating Etruscan-specific quirks and some with barely any surviving information.
You mentioned the Etruscan divination system, so we'll touch on that really quickly before we go! Really, it's systems; divination was a centrally important religious practice for them, and there were several different types of divination that could be called upon to help understand the world. Haruspexy, the practice of divining from the entrails of animals, was popular (and later remained popular when the Romans took it up), and other forms of divination included the scattering of metal leaves or sacred plates and interpreting the symbols on them, divination from interpreting the lightning strikes in storms and high-air weather, and divination from the croaking of frogs or singing of birds. The entire world was constantly revealing the will of the gods, as far as the Etruscans were concerned, so they spent considerable time and energy trying to figure out it was trying to say.
Interestingly, they didn't, as far as we can tell, have any really strong way of organizing their constant reading of signs and portents. The Etruscan philosophy was to read as many signs from heaven as possible, and try to cobble them together into a guide for living life with the best fortune possible and the best knowledge of the future that they could come up with. Divination was widely understood to be an inexact science, one that both regular people took part in for their daily lives and priests in an official capacity only slightly more accurately... so obviously, the more signs you could read, the greater your chance for getting something right!