Buy 1 and get 1 free of the same product
Buy 3 and get 1 free Offer that will start at some time in future
Buy 1 and get 2 free of different product
Buy 1 and get 1 variable product free (you can change variation of the free product)
Buy 1 and get 1 with option to select the 1 free product from list of products
Category based rule
Buy product from category get product B free