Master Products allows you to assign a product as a 'master', and other
products as slaves (or not at all) - eg. if there is a product range with
individual items that each may be purchased separately. These all display listed below the master product in product_info with a quantity select for each
item, and a single add to cart button.
Whether the slaves show in the main product listing is selectable on the product edit page in admin. Master Products and 'shown' Slave Products link to product info from product_listing and new_products, rather than directly to the cart (buy now) - zero dollar amounts for Master Products do not display.
Slave product listing display is selectable in admin>configuration in a similar manner to the product_listing page under the 'Slave Listing" options. A truncated product description (by John Poynton - Description in Product Listing) is also selectable. Product attributes in the slave product listing will be available in the next release.