PrestaShop

PrestaShop is an open source e-commerce platform that gives merchants full control of a storefront, covering catalog, pricing, stock, orders, shipping, and customer accounts. It adds a large marketplace of modules for payments, carriers, marketing, and SEO, supports multiple languages and currencies, and can run several shops from one installation through its multistore feature.

Retailers choose it to sell directly rather than paying a marketplace commission.

Hosting it yourself keeps customer and order data in your own database, and your only recurring cost is the server you run it on.