Persistent Cart ‑ Sync Devices

This app really differentiates itself from others in the app store by a) using a nice modal popup rather than a javascript alert, and b) in a conflict allowing the customer to choose whether to keep their current cart, restore their previous cart, or merge the two.

The interface for the customer could use some work, but I was able to fix most of my complaints with some custom css. All in all, well worth the price!