This extension is a ‘wrapper’ for NOP's Free Shopping Cart:
http://www.nopdesign.com/freecart/
NOP’s Shopping Cart is a client-sided cart implemented with JavaScript with many features!
http://www.wysiwygwebbuilder.com/nopcart.html
You can download the new extension through the Extension Manager (Menu->Tools->Extension Manager->Available).
Note that this extension is experimental (because of its complexity). It is provided "AS IS" for those that find it useful.
Please read the help...
Merry Christmas!