Easy to configure BOGO Discounts for Zen Cart

A surprising number of people have asked for Buy One Get One Free or Buy Two Get One Free style discounts for all products in their cart (either for the same product or for products of lesser or equal value). You can do this with Big Chooser (see examples 7 and 8 in Advanced Configuration of That Software Guy’s Zen Cart Discount Modules), but it requires writing a specific customization that makes it hard to easily switch to a different policy (say, Buy One, Get One half off) the next month. So I created BOGO Discount for Zen Cart, a module that lets you easily create “Buy some-number-of-X, get some-number-of X at a reduced price” style discounts – for identical items, items in the same category, or items without restriction.