OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
Sellbeing - Simple e-commerce website builder.
EvenCart - EvenCart is an open source hybrid/headless eCommerce software built on top of ASP.NET Core and Shopify Liquid.
nopCommerce - nopCommerce is the open-source eCommerce solution. nopCommerce is available for free. It has everything you need to get started in selling physical and digital goods over the internet.
Paperform - A digital Swiss Army Knife for Small Businesses
Jumpseller - Start Your Online Store! Grow your business.