Here's a quick list of some Drupal 7 modules that have been created to interface with Ubercart.
I'll create a post for each one where you will be able to vote for the ones you would like to use in Ubercart for Backdrop CMS.
Bank Transfer | Ubercart Payment
https://www.drupal.org/project/uc_bank_transfer
This module provides an Ubercart payment method. It helps to display the shop's bank account details to the customer so a direct money transfer can be initiated by the customer. Depending on where you are from you might call this method bank transfer, wire transfer, giro transfer or direct deposit.
Ubercart Affiliate Product
https://www.drupal.org/project/uc_affiliate_product
Need to add specific products to your Ubercart product catalog that are only available for purchase through an affiliate's website, rather than directly through your own?
Ubercart Affiliate v2
https://www.drupal.org/project/uc_affiliate2
This (uc_affiliate2) is a module providing affiliate functionality for Ubercart.
Ubercart AJAX Cart
https://www.drupal.org/project/uc_ajax_cart
This module provides a drop-in replacement for the default Ubercart cart block that is entirely AJAX enabled, allowing users to add, update or remove items from their cart without needing to refresh the page.
Ubercart attributes in cart
https://www.drupal.org/project/uc_attributes_in_cart
This module allows site administrators using the Ubercart and its Attribute modules to let their visitors change the attributes of products they have added to their cart on their cart page.
Ubercart Bulk Attributes
https://www.drupal.org/project/ubercart_bulk_attributes
The idea of this module is to give the option to create a lot of attribute options for a specific attribute at once, and optionally add them to 1 or more products.
Ubercart CSV https://www.drupal.org/project/uc_csv The purpose of this module is to export orders from an Ubercart store in a manner that can be read by any spreadsheet program including Microsoft Excel.
Ubercart Custom Sized Products
https://www.drupal.org/project/uc_custom_sized_products
The Ubercart Custom Sized Products module will allow store owners to sell products with custom dimensions. For example, if the store wanted to sell carpet by the square foot or to sell rope by the foot. The module will calculate the length, area, or volume and will multiply that number by the price set for the product.
Ubercart Discount Coupons
https://www.drupal.org/project/uc_coupon
This module provides discount coupons for Ubercart stores.
Ubercart Discounts (Alternative)
https://www.drupal.org/project/uc_discounts_alt
uc_discounts_alt is a full-featured Ubercart discounts module that supports both code-based (i.e. coupons) and codeless discounts.
Ubercart Early Bird Discount
https://www.drupal.org/project/uc_earlybird
This is a discount module for Ubercart which allows for date-based discounts without coupon codes that can be set per node at product creation.
Ubercart Fee
https://www.drupal.org/project/uc_fee
Ubercart Fee lets you add additional fees to Ubercart Products. Fees are configurable at both the product class and the product level. Each fee appears as an individual Line Item in your Order.
Ubercart Feed Mappers
https://www.drupal.org/project/uc_feeds
This module provides Feeds mappings for Ubercart items, including model, prices, weight and weight units.
Ubercart Field attributes
https://www.drupal.org/project/uc_field_attribute
Ubercart Import
https://www.drupal.org/project/uc_import
This module allows you to import product, taxonomy terms, attributes and images/files from a .csv file. Since the procedure of importing data into Ubercart is particularly delicate, any suggestions would be very welcome.
Ubercart Importer
https://www.drupal.org/project/uc_importer
The Ubercart Importer uses an XML format to import and export Ubercart's product catalog into the Drupal site. The current version supports the following:
Ubercart Invoice payment
https://www.drupal.org/project/ubercart_invoice_payment
This module will give Site admin the ability to create invoices for customers and customers will receive the link in the mail to pay the invoice.
Ubercart Limited Time Offer
https://www.drupal.org/project/uc_lto
Ubercart Limited Time Offer adds functionality to Ubercart to make a product available for a limited time in a variety of styles - time of expiration, time remaining, active countdown, etc.
Ubercart Manufacturers
https://www.drupal.org/project/uc_manufacturer
The manufacturer module lets you list manufacturers in a taxonomy vocabulary and assign them to products. It also adds a few manufacturer-specific pages and form settings to store the information you might require for your product manufacturers.
Ubercart Marketplace
https://www.drupal.org/project/ubercart_marketplace
Ubercart Marketplace adds multiple seller support to the Ubercart module. It includes a series of modules that limit access to Ubercart functions for sellers.
Ubercart Min/Max Order Quantity
https://www.drupal.org/project/uc_moq
This simple module allows Ubercart store administrators to set the minimum and maximum number of items to be in the shopping cart before a user is allowed to proceed to checkout.
Ubercart Organic Group Subscribe
https://www.drupal.org/project/uc_og_subscribe
Ubercart Organic Group Subscribe makes it possible to sell Organic Group membership to one or more groups when a user purchases a particular product. uc_og_subscribe implements Ubercart features, making it possible to have the purchase of one product result in a subscription to one or more other groups. Subscriptions can be configured as regular or admin subscriptions.
Ubercart Out of stock Notification
https://www.drupal.org/project/uc_out_of_stock
It uses ajax and jquery and asks the server for available stock and replaces the 'Add to cart' button with some configurable HTML.
Ubercart pictured cart block https://www.drupal.org/project/uc_pic_cart_block Our pictured cart block provides some advantages in contrast with the standard Ubercart block.
Ubercart Price Per Role
https://www.drupal.org/project/uc_price_per_role
This module allows you to enter different sale prices per product for different roles in an Ubercart store.
Ubercart Product Actions https://www.drupal.org/project/uc_product_actions If you have lots of products in your shop, and you ever wanted to do any of the following, this module will surely help:
Ubercart Product Expire
https://www.drupal.org/project/uc_expire
This is for Ubercart sales. Some products, like event tickets, have dates beyond which we do not wish to sell them. This tool allows sales to be automatically disabled on a pre-set date.
Ubercart Product Power Tools
https://www.drupal.org/project/uc_product_power_tools
Product "Power Tools" for Ubercart allows the store admin to hide, disable or preset certain options (SKU, price, quantity etc.) in the Ubercart product creation form.
Ubercart Register Invoice Templates
https://www.drupal.org/project/uc_register_invoice
This module finally gives a good answer to the common question from Ubercart administrators: "How do I customize the e-mail invoice sent to customers after they make a purchase?" This module also makes it easier to send different or multiple e-mail messages under different circumstances.
Ubercart Restrict Qty
https://www.drupal.org/project/uc_restrict_qty
Ubercart Restrict Qty lets you add a very basic Restrict Qty. to a product in your Ubercart store to limit the quantity of that product in the shopping cart to 1. This is useful for single-purchase products or for instances where it just doesn't make sense for a customer to purchase more than one and you want to prevent it from happening.
Ubercart Services
https://www.drupal.org/project/uc_services
This module will integrate Ubercart with the Services module so you can control your Ubercart from remote software/sites or use it for synching Ubercart sites with each other.
Ubercart Simple Discount
https://www.drupal.org/project/uc_simple_discount
This module aims to provide a simple approach to automatically applying discounts in Ubercart.
Ubercart terms and conditions
https://www.drupal.org/project/uc_tc
This is a simple module that adds a checkout pane to the Ubercart checkout page to force the user to agree on the site's terms and conditions.
Ubercart Terms of Service
https://www.drupal.org/project/uc_termsofservice
This module includes an Terms of Service text (aka terms and conditions) and a [x] I agree with the Terms of Service checkbox for the cart or the checkout page of the purchase using Ubercart.
Ubercart Ticket
https://www.drupal.org/project/uc_ticket
Ubercart Ticket is a ticketing/customer support system for Ubercart.
Ubercart Views
https://www.drupal.org/project/uc_views
This module provides a collection of standard views (http://drupal.org/project/views) for the Ubercart webshop module (http://drupal.org/project/ubercart). It also describes some of the Ubercart data tables to views, so you can create your own views, based on these data using the views_ui.
Ubercart Volume Pricing
https://www.drupal.org/project/uc_volume_pricing
Ubercart Volume (AKA Bulk) Pricing allows you to define discounts on buying a product in mass quantities directly from the product edit itself. For example, if you want to have 'Buy X products and you save Y dollars'. The module allows for an unlimited amount of bulk entries per product
Ubercart Webform Checkout Pane
https://www.drupal.org/project/uc_webform_pane
This module allows you to define Webform nodes as checkout/order panes in Ubercart.
Ubercart Webform Integration
https://www.drupal.org/project/uc_webform
This module integrates two other modules: webform and Ubercart. It allows you to sell products directly from your webforms. It is particularly suited to be used as part of a registration system.
** Issue cue says not compatible with Webforms V4 **
UC Attribute Stock
https://www.drupal.org/project/ubercart_attribute_stock
This module works with the attributes of products. It allows you to combine several attributes info one and keep track of stock level.