Yep, free code, the best kind !
But it works the other way around, you get the free code and then integrate your site into it. Basically, it comes with a whole shoopping site solution, and you just then customize it to look like you want.
Three of the most popular are:
http://www.opencart.com/
http://www.oscommerce.com/
http://www.zen-cart.com/
Now, if you look at the
out-of-the-box solution of oscommerce it doesn't have anything about it that would make customers want to stay. However, you can customise it look like you want. i.e change it to look
like this
You can choose any solution you want, and if you don't have the skills to change the template yourself you can pay someone to do it for you. A great website is
get a freelancer.
Another option for you is to use either
google checkout or
paypal pro or any other cart solution i.e.
nochex
Good luck.