The Buy One Get One Free plugin allows to create offers of the type: if the customer adds to cart a specific quantity of a product, then give away one or more items of the same or another product.
Some examples of promotions you can create with Buy One Get One Free:
Buy One Get One (or BOGO for short) is one of the best offers you can use to clear out and move inventory, and also to generate more cash. People have to buy more to get the offer, so you get more cash.
The Buy One Get One Free plugin include functions and features that cover a broad range of use cases.