The Recover Cart Sales plugin is a very handy tool for addressing abandoned shopping carts. Every store has them but the default Zen Cart installation does not provide any way to address them.
With the Recover Cart Sales plugin you are now able to contact shoppers who added something to their cart and got far enough to register (so you have their email address). While some never intended to place an order, some did but did not have all the information they needed to complete the order. For those, this will allow you to resolve those issues and close the sale.
For more details about this plugin, please see our blog post Recover Cart Sales plugin for Zen Cart