It appears the people behind X-Cart (qualiteam) have just released a beta version of their hosted AJAX/Gears based E-Commerce package. The package is free however it is a hosted solution with Amazon’s cloud hosting or EC2 web service for data storage. Some of the cooler features is the Drag and Drop functionality for items to your basket. Mobile version with static HTML Catalog for SEO purposes as well. It is widget based so it can easily be dropped into any CMS system.
The biggest downside it seems to such a solution is there is no means currently to have a custom solution, via API or through Qualiteam themselves. The Cart is visually customizable via CSS within the admin but I’m guessing it won’t be very “in depth”. Also there is no manual.
On the plus to all these items though is it is FREE 
Possibly Related Posts:
- Magento Commerce Error Reporting Tip
- Android SDK 2.01 Emu WebKit User Agent
- Eclipse + ZendStudio + ZendServer + Android SDK = Awesome IDE
- Magento: Phoning home to Big Brother/Varien?
- Selecting 30 days or older entries using MySQL DateTime field
Good explanation of Ecwid idea can be found at http://www.ecwid.com/forums/showthread.php?t=24
Have you ever seen a google store gadget?
http://storegadget.googlelabs.com/
Have not seen the Store Gadget before, thanks for pointing that out.