OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
Pennywise - Cross-platform application to open any website or media in a floating window
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.
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Gumroad - An all-in-one solution to sell your work and grow your audience.
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.