When last I blogged about Outdoor Cat in May, she had just survived the Wisconsin Humane Society's Trap-Neuter-Return program. Over the summer, we worked on socializing with her and getting the two indoor cats Nuts & Ruby used to her presence. (That's Nuts on the left above, and OC on the right, each pretending the other cat doesn't exist.) OC started coming inside briefly after one day following me in the front door when I took her dish inside to change the water and refill the food. Pretty soon she figured out that the indoor cats ALSO had food and water! She would come inside to look around but would quickly run out again if she was startled.
We still weren't sure whether we would try to bring her inside for the winter or not, but we figured we'd try to get her litter box trained in a kennel for the really cold nights, just in case. I borrowed a dog kennel from my sister and kept OC in it overnight in the spare bedroom for the first time on Halloween, when 200 neighborhood kids invaded her territory on our front porch.
She handled the litter box OK but was not keen on the kennel, trying to tunnel out of it. When we were sure she would use the box, we experimented with leaving the kennel door open. She still preferred to be outside, so when our first big snow was predicted, I invested in a SnuggleSafe Microwave Heat Pad
for her shelter. However, after we brought her in out of the storm, she settled in to her new space in front of the heat vent. 
So she's been living indoors since mid-December, occasionally looking outside but thinking better of it after a minute or so in the cold. She's even trained us to leave her bedroom door open for her (after repeatedly waking us up at ungodly hours by scratching at it) and now she guards the upstairs hallway at night. Since Nuts sleeps on our bed, there are occasional rumbles in the wee hours when they cross paths in the hall. (Ruby sleeps all night in the living room and generally ignores OC.) We have been closing OC's bedroom door during the day when we're at work, so when we come home and let her out, she will sometimes run downstairs and ask to go outside, look out the front door at the snow and ice, and run back upstairs to her food dish. We are not ruled by cats, at all. Honestly!
