OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
Kajabi - Kajabi is the only Knowledge Commerce platform today with everything you need to market, sell, and deliver your knowledge online.
Gumroad - An all-in-one solution to sell your work and grow your audience.
Tendenci - Tendenci - The Open Source AMS is a cloud-based all-in-one management SaaS solution for Non-profits and Associations.
Shopify - Shopify is a powerful ecommerce platform that includes everything you need to create an online store and sell online. Try it free for 14 days.
YourMembership - YourMembership provides membership management software integrated with social networking features.