OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
ASAAS - ASaaS develops software to automate the control of subscriptions, billing, recurring payments, and digital signage.
PayKickstart - PayKickstart is the ultimate shopping cart and affiliate management platform, empowering online Entrepreneurs and digital publishers with the tools to sell their products online.
Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.
Gumroad - An all-in-one solution to sell your work and grow your audience.
GoSpaces - Sell subscriptions services, digital downloads and physical goods with no hassle. It's free to use!