Tomatoes can keep producing fruit well into fall, but they need temperatures of 75 degrees or more in order to reach full growth and optimum ripeness. Therefore, most tomatoes that start growing in the fall stay small and green. Don't throw them out, though.
Unripe green tomatoes are edible, and can be used to make all manner of tasty treats. Last year, we had a Green Tomato Contest where readers submitted their favorite green tomato recipes. The winner was Tonia's Eggs Benedict With Green Tomatoes. You can peruse the other contest recipes at this link.