Give Free Product


Is there an way to setup the CS_cart, or perhaps an addon that can give a free product to a customer for each and every purchase, of say 5 or six items of the same product?

Say customer buys 5 small black socks, and then gets 1 more black sock?
Or a customer buys 15 blue hats, and then gets 3 free blue hats?

Kind regards

maybe this could work for you