Amai PreOrder Manager + Notify

Stellar. This app is key in our import and distribution operation as we have multiple warehouses worldwide. By using "Pre-Order" as a back-order enabler, we're able to accept orders for inbound products on an ongoing basis, even if the stock is not readily available. The built-in messages and tooltips help us align expectations with our customers and reduce support calls.
Other than that the app support is incredible - always going the extra mile to make sure we're happy!