If you are interested in Zen Cart, you might want to have a look at ZenMagick
ZenMagick is a zen-cart add-on that includes:
1) An object-oriented API to access the zen-cart database (anywhere in your code).
Example:
$product = ZMProducts::instance()->getProductForId(3);
echo $product->getName();
2) An alternative templating system
Building on the API, the template files are a lot simpler that their zen-cart counterparts. The code is (also) object-oriented and includes a fill MVC stack. Also includes are:
- a (form) validation subsystem
- plugins
- support for many popular zen-cart mods (IH2, etc)
There are also unique ZenMagick features like:
- checkout without registering
- support for OpenID
- page caching
- Support for Smarty templates
ZenMagick is licensed under the GPL.
Cheers, mano
(disclousure: I am the main developer of ZenMagick)
Unsolved 
