This plugin allows you to reduce shipping rate dynamically according to products in the customer cart.
Each product can donate a value to reduce shipping rate, so if there are two products in the cart, one with 2.00 of discount and another with 3.00 of discount, if the shipping rate is 17.00 this plugin will reduce shipping rate to 12.00.
The idea behind this plugin is to improve your sales by transferring the shipping rate to product price avoiding customer to abandon on the checkout/cart page.