Tierly: Buy X Get Y Free

Most buy-one-get-one apps use a single fixed ratio. Tierly lets you define your own quantity tiers — for example, a customer's 3rd eligible item free, then buy 2 get 2 free repeating from the 4th item on. Pick eligible collections, set your tiers, and the discount applies automatically at checkout — no codes needed. The cheapest eligible items are always the ones marked free, protecting your margins. Combines cleanly with order-level promotions like a welcome discount.