Amai PreOrder Manager + Notify

Update, 12-31-16: They've made that change (below) due to my suggestion. Good job guys! Thank you for valuing your customer's feedback.
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Update, 12-26-2016: Many thanks to P.Z. from support for helping me install the id for my add to cart button in my liquid files. It was a tedious task and I only hope Pre-Order Manager can automatically make this change once you switch over to a new theme ...

Works very well, simple and effective.

Great and simple app, that is free and does what it says it does. So grateful to not have to pay for this feature, when these days any added funciton in Shopify requires more $$.

The app is awesome that help me generate plenty of sales. Had an issue with the app but their customer service is first class. Got it solved within the day.

Really great, does exactly what you need it to do and has great control over how many products can be pre-ordered. Customisation of pre-order buttons and messages on individual listings is good too. Only thing that could be better is to have an option to stop pre-orders on a certain date. Thanks!

EDIT: the developers added that feature really soon after I posted this review! would upgrade to 6 ...

The support team was very responsive and super helpful with making custom updates to the app. Thank you!

Great app with a great team behind it. They helped me get it all set up with my theme nice and quickly, and are working to add more features as we speak. A great option for accepting pre-orders on your shopify store!

This is truly an amazing app!! It works great and solved a hug problem for us! Would definitely recommend.

Love this app! Makes our pre-orders perfect.

This app works great and also the out of stock notifier app that they make is awesome. extremely fast customer support!!