DiscountYard — Stack Discounts

Allows you to use two+ discount codes on the same order. Would be preferred if Shopify just could do it natively, but this app works wonders. You can only use the discount codes within the cart discount line (not the checkout), but not going to knock down the app rating as it has to do with Shopify's system. I do also want to give a plug that the support is fantastic. Gets back within 15 mins or so (this is US normal business hours) and fixes any issue that is occurring.