In recent news, Honey, the online coupon code web app is reportedly being bought by Paypal for $4 Billion. Honey has a web app, or "plug-in" that works with your browser to find and apply coupon codes for whatever website you are shopping on.
After a user installs the Honey plug-in, a Honey widget will appear in a browser at a shopping website's "checkout" (see celebrating coin above). The screen-grab above is from a GAP checkout page. In this case, after applying the 6 coupons, no savings were realized. I think the particular blue jeans that were in the shopping cart were not part of GAP's latest 40% promotion.
The founders, George Ruan and Ryan Hudson, apparently have a few patents relating to their core technology, including US10140625B2. In this patent, the claims relate to the workings of their online coupon assistant. For example, claim 1 of the Honey patent recites: "upon the user's selection of the graphical trigger, automatically input each of the one or more digital codes..., thereby triggering the third party website to receive the one or more digital codes... and apply the digital code that causes the greatest change in the numerical value to obtain and display a resulting numerical value on the third party website."
The flow chart below (Figure 9 of Honey's patent) gives a simple description of how Honey works. Perhaps all the average user needs to know is install, then save.