Zen Cart

Zen Cart is a shopping cart based on the old oscommerce engine but it offers tons of more features and has an active support community. You can use this to sell items over the internet*. You can visit Zen Cart's website for more details and to see examples of it being used. http://www.zen-cart.com/.
 * You will still need to make arrangements for receiving and processing payments in a secure manner

Zen Cart is an increasingly-popular open source shopping cart system written in the PHP programming language. It is available to DreamHost users as a One-Click Install.

Dreamhost Zenners check this thread so you can fix a serious customer login session bug that only seems to happen on Dreamhost: http://www.zen-cart.com/forum/showthread.php?t=37465