https://apps.shopify.com/product-add-ons
Create add-ons for one or more products
Create add-ons for all the products in the catalog (Useful for things like adding a Gift wrap add-on to all products)
Create add-ons for collections
Create popup add-ons
Guide to Improving performance
Guide to available setting options
Guide to configuring add-ons on Shopping Cart Page (Only Applicable to Utilmate Edition)