OSCommerce is a set of programs allowing you to start you own on-line business very simply. You can enter your products and setup shipping and payment in a few hours. OSCommerce works with major payment gateways such as Authorize.Net and Pay Pal to allow you to accept credit cards on-line.
As you gain experience you can add features and enhancements; OSComerce is made with PHP and there is an active community of developers around the world.