Check with your local animal control office or humane society to see if they have a trap-alter-and release program. Many communities have these now. The idea is to spay and neuter the feral cats and then let them live out their lives where they were found.
If there is no such program in your area, or if you don't want to be involved with it for some reason, some people catch feral cats and have their own vets alter them.
After that, you can always provide good food and clean water for them if you wish.
I have mixed feelings about this issue which has given attention to feral cats. Feral cats have been existing and thriving throughout the ages of time. Without domestication, all cats would be feral. The few domesticated cats who we host as our pets to indeed indicate their needs for our care. Cats who are outside on their own do need to be sustained the way that any other animal in the wild needs to be cared for. Nobody is out to sterilize squirrels, though. Animals out in the wild have their ways of surviving. I do not see any issue about feral cats, other than what I feel may be politically fabricated. I feel concerned about the trends I see locally. There is not only a campaign in Los Angeles to sterilize all feral cats, but domesticated cats too, by statute. This I fear could lead the way to domesticated pet black markets. To create a commercial value to cats to purchase and to inflate prices of cats. I do not pity a feral cat. But I am in favor of offering a feral cat a stable location of human-provided food.