Go to https://demo.teacommerce.net/ and try Tea Commerce - both the front-end and the back-office.
Build on top of Umbraco
Tea Commerce use Umbraco's content section to manage product categories, products, variants etc.. This allows you to build the entire Umbraco ecommerce solution via content nodes, document types, views, partials, CSS etc., and when you're ready, install Tea Commerce and you can implement the shopping cart, order flow, payment with credit cards, etc. Thats it!
Use existing Umbraco packages
Tea Commerce is build using the Umbraco API and therefore 100% compatible with other Umbraco packages. With all the packages already available for Umbraco, you can extend your Umbraco ecommerce solution indefinitely and create entirely new functionality never before seen in a webshop.
Need more info? See http://www.teacommerce.net
Tea Commerce supports Umbraco 6+ and MS SQL, SQL CE, MySQL and Azure SQL
Updating Tea Commerce
Important - You can't upgrade a Tea Commerce 1.x to 2
Updating is as simple as re-installing the package.
Always check the revision history before updating.
Tea Commerce Starter Kit
The starter kit makes it really simple to try Tea Commerce or show it off to a client. It's a fully functional webshop that is ready to use.
Documentation - https://documentation.teacommerce.net/
Feature list - https://teacommerce.net/products/tea-commerce/
Revision history - https://documentation.teacommerce.net/revision-history/