https://arstechnica.com/gadgets/2017/12/customers-now-preorder-apps-in-any-apple-app-store/

Apps are just as highly anticipated as other forms of entertainment now, and Apple's newest update to its app stores let customers call dibs on their favorites before they're even released. An update to the iTunes Connect resources page states that developers can now open up their apps for preorder on all Apple platforms before the program is officially released. This allows developers to see the product page before anyone can download the app, and customers can tap a new "Pre-Order" button to secure their download before it becomes available on the designated release date.