Community cats, also known as feral cats, are unowned cats who live outdoors in groups. Although they are the same species as your pet cat, they are typically not socialized or friendly towards humans. The only humane and effective approach to community cats is known as Trap-Neuter-Return (TNR), and it helps both the cats and the neighborhoods where they live.
In the TNR approach, community cats are trapped, spayed or neutered, vaccinated, ear-tipped for identification and returned to their outdoor home. This program compassionately manages community cats through non-lethal means. Existing community cats become healthier and easier to to track, and the number of cats will decrease due to a decline in birth rates.
What to do if you find a stray cat: http://www.saveacat.org/find-a-stray-cat.html
Feral vs. Stray Cat: http://www.saveacat.org/feral-vs-stray-cats.html
What is TNR?: http://www.saveacat.org/tnr---what-does-this-mean.html
Constructing a Basic Cat Shelter: www.saveacat.org/providing-shelter.html
Guide to Safely Relocating Feral Cats: http://www.saveacat.org/relocation.html
Tips for Protecting Cats in the Winter: http://www.saveacat.org/winter-tips-for-protecting-cats.html
Tips for Protecting Cats in the Summer: http://www.saveacat.org/summer-tips-for-cats.html
Feral Cats and the Law: http://www.saveacat.org/feral-cats-and-the-law.html
Cat Overpopulation: http://www.saveacat.org/cat-overpopulation.html
Source: Alley Cat Rescue Website