To simply put it, it allows for you to give attributes a quantity. I know a few people that use this shopping cart that wished that it had this option so I thought I would write a modification to do this. Once you have added an attribute the quantity option for the actual product is disabled. This mod will control your product stock levels so everytime you add or delete a product attribute the total quantity will change accordingly. If you delete all attributes for a certain product you will have access to the standard quantity control again. Once a product attribute has reached a quantity of 0 it removes the product attribute from the product page. Future development might include more options for this. Thanks to Pavel Rojkov I have added his contribution to allow you to manage product attributes from the products page.