The Silverstripe Cataqlogue provides an interface to create and manage "Products" and "Categories" in isolation of the CMS module.
Most ecommerce systems provide a tabular interface to easily manage product catalogues (including bulk import, export and alterations), but most Silverstripe modules seem to focus on turning products into a type of page object (therefore requireing the CMS module).
If the CMS module is installed, then this module will attempt to correct URL's of products and categories so that they do not intefere with Page object URLs.
NOTE Please be aware, this module only provides a product catalogue to Silverstripe, including Stock ID's, prices, SEO friendly URLS, etc.
If you want full e-commerce, you will need to add the orders and checkout module (or install the commerce module instead).