List of some popular free ecommerce platforms that you can consider for your digital marketing shop:

1. Shopify

Though not entirely free, Shopify offers a 14-day free trial period which can be a good starting point for your business. It's user-friendly and offers a variety of customizable templates.

2. WooCommerce (WordPress)

If you're familiar with WordPress, WooCommerce is a great option. It's an open-source plugin that integrates seamlessly with WordPress, allowing you to turn your website into a fully functional online store.

3. Big Cartel

Big Cartel is geared towards independent artists and makers. It offers a free plan that allows you to list up to 5 products, making it ideal for small businesses.

4. Square Online Store

Square offers an easy-to-use ecommerce platform that integrates well with its payment processing services. It's free to use, with options to upgrade for additional features.

5. Wix eCommerce

Wix is known for its drag-and-drop website builder, and it also offers ecommerce functionality. While not entirely free, it does have a free plan with limited features, which can be suitable for small businesses.

6. Ecwid

Ecwid is a popular choice for adding ecommerce functionality to an existing website or social media page. It has a free plan that allows you to list up to 10 products.

7. PrestaShop

PrestaShop is an open-source ecommerce solution that offers a free, downloadable software. It provides a wide range of features and customization options for building your online store.

8.  Magento Open Source

Another open-source option, Magento offers a free community edition that is feature-rich and highly customizable. It's more suitable for businesses with larger catalogs and more complex needs.

9.   OpenCart

OpenCart is a free, open-source ecommerce platform that's easy to set up and use. It offers a variety of extensions and themes to customize your online store.

10.   Spree Commerce

Spree Commerce is a customizable and scalable open-source ecommerce platform built with Ruby on Rails. It's free to download and use, but may require technical expertise for customization.

These platforms vary in terms of features, scalability, and technical requirements, so it's important to choose one that aligns with your business goals and needs.