Unfortunately, not all cats are blessed with warm homes to live in. Which is OK by some of them. Many cats live outdoors as feral cats. They have to find shelter, water, and food in the winter which could be more difficult than it is in warmer months. The nice thing is that people can help.
If there's a feral cat or feral cat colony near where you live, you can always leave out some extra food for them. That's a nice way to help. Or you can even build them a shelter. A shelter for feral cats doesn't have to be too fancy. You could make one out of all kinds of things if you get creative enough.
This article at Petfinder tells you how to build and maintain a feral cat shelter. There's also a video there with some more tips.
In areas where the temperatures get below freezing, water can be hard to come by for a feral cat. There are heated water bowls you can buy fairly cheap that can keep the water from freezing. Here's another great article on how to prevent freezing water.
Don't forget to check your car for cats before you turn it on. Cats like find shelter in car engines and on wheels when it's cold outside. All you have to do before you get in your car in the morning is take a once around your vehicle and knock on the hood. A feral cat should get the idea and run away from any sort of danger.
I've unfortunately witnessed firsthand what an engine can do to a cat. It happened once when I was probably in middle school. The cat suffered a broken leg from what we were able to tell. She ran off to hide and never let us take a good look. But the cat did live for many years afterwards, thankfully. Her name was Banshee because she was a pretty wild one.
Anyways, with just a few simple steps you can help a cat keep warm and well-fed in the winter. Even if you only did one of the things on this list, it will probably help out tremendously. It's cold out there friends, so stay warm!