The Free Shopping Cart software from Avactis is a great way for any online merchant to start selling online without much investment. PHP-based, suitable for pretty much any modern hosting, embeddable in existing PHP sites, it can quickly get you started. And should you need additional features of the full package, you can upgrade anytime and keep all products, orders, and customers you gain by that moment.
Downloadable package — install on your server
No time limitation (does not expire)
No credit card required to download
Open source code (no encryption/obfuscation)
Accept online payments via PayPal
Upgrade to the full version anytime without losing any data