Sounds like a domestic cat. Here in the UK my mother's cats used to catch rabbits and would happily eat the skin and bones along with the rest, but frequently left the digestive tract and sometimes the head, presumably because those were the least tasty bits. While I've never seen fur left arranged in a ring, there ususally is some fur around after a cat kills anything fluffy because they'll grapple it with their paws and often play with it for a while, meaning fur gets pulled out.

I've made similarly grisly discoveries in my backyard - possum stomach/entrails and absolutely nothing else, and the same with some of the rear end still attached (and the smell has never quite vanished - I still get whiffs of it now and then...)  Cats definitely high on the list on suspects - there's often possums running helter skelter along the fence/roof here with something in hot pursuit and I've caught local cats prowling my yard - one even had the cheek to have a drink out of my bird bath!  I had wondered about Powerful Owls but have never seen or heard any trace of those here.

I hesitate to contribute, because I know so little about Australian natural history. I agree with the possibility of cats, and they seem to me likelier than birds of prey, for two reasons: although the discarded fur is consistent with the feeding behaviour of avian raptors, I don't normally expect birds of prey to spare the guts particularly, and secondly, if they leave bones, the bones usually are largely entire.

Cats on the other hand, often leave only the harder parts of bones, the remainder having been chewed off. Accordingly it is not unusual to find just the tooth bearing parts of the jaws of mice and similar prey.

Some wise people have said: "When you hear hoof beats, think of horses, rather than zebras." On that basis I must support the cat vote, but have you eliminated the possibility of another local, predatory or omnivorous species of marsupial? in the Americas some species of possum would fill the bill, but in Australia I should not be really badly surprised if you had been favoured by visits from other predatory marsupials such as quolls. They might well regard say, sugar possums as convenient means of converting nectar into quoll.

Just in case it might be a quoll, please do not go putting out traps or poisons before the culprit is identified. Sydney is in quoll territory according to the map at my disposal, and it would be dreadfully upsetting if you killed one by mistake.

Especially during daylight, I don't think your children and larger pets should be in any particular danger, whether from cats or quolls. Phone the zoology Department of the nearest university and ask someone for an opinion. The pattern of feeding sounds very characteristic and should provide useful clues to any local zoologist. If it does indeed prove to be quoll work, I am sure they would like to know about it, and so, certainly, would we.

As I work in Melbourne, Australia, I've come across the entrails of possums numerous times over the years, The usual pattern I see is fur, stomach and intestines. My curiosity got the better of me and I found this page.

I susepct owls but it could be also be foxes, cats or dogs. I think the entrails of herbivores left behind is the signature of the indigenous carnivore but I can't be sure.

I'm leaning more toward a airborn predator but as possums come to ground to move between trees I can't discount 4 legged predators. The reason I suspect birds is because they are the natural predator.

The known owls in the area, that I have seen, are Barn Owl and Tawny Frogmouth. At the same time I cannot discount the presence of Powerful Owls and Boobook Owls (which I have heard) as they are known hunters of possums.

I'd be interested if someone can shed more light on the mystery.