You can get a free Wendy's cheeseburger with any purchase once per day through 9.30.18 by downloading Wendy's smartphone app (iTunes iOs or Google Android) and checking the Offers tab. While you have to make a purchase, you're still getting a burger for the price of a junior fries or small drink!
Note you can reuse this coupon once per day for the entire month of September. Not that I recommend it! Good God, man, think of your arteries!