Appstle℠ Bundles & Discounts

Surprisingly thorough for a free app! You can build many types of bundles and discounts with very specific rules, which was very helpful for organizing the complex discount structure on my store. Support is very prompt and can help you with customization. My only small disappointment is that you can't change the way that costs are displayed on volume discounts in particular, i.e. if you want to display the cost per unit rather than the total cost of a specific number of items that is not possible with the current app structure.