Extra Product Fields allows you to create new fields for information for your products. The fields can either be text fields where you type information directly into the field (either single line or multiple line) or list fields where you choose a value from a list of predefined values. You can create list fields that will either allow you to select only a single value or you can have a field that allows selecting multiple values from the list.
After a long time and a lot of work I've finally updated my Extra Product Fields contribution to work with osCommerce 2.3x. New features include the ability to choose where extra field information will be displayed in the catalog including the specials listing, new products listing and shopping cart as well as the original product listing and product information page. You can now choose to store field information in orders as well. Information needed for a Google Product Feed is now also included and certain fields needed by Google are automatically added to your products. The list type fields now support proper multi-language capabilities. The Google Feed portion includes a utility to update the list of Google product categories when needed. The feed creation tool now allows you to assign product attributes that aren't already included in the feed to any product field not already used by another attribute, including the new extra fields you create, and have that attribute added to your product feed. This should come in handy for those selling products like apparel that require more attributes to be set that other products.