https://apps.shopify.com/tightly-io
Tightly: Inventory Planning - AI-driven replenishment, PO automation & backordering | Shopify App...
inventory planningai drivenpo automationtightly
https://www.bigcommerce.com/blog/backorders-beta-announcement/
Backordering Now in Beta for All BigCommerce Merchants
Introducing Backorders, a new beta feature that helps merchants continue selling after stock runs out with built-in limits and inventory tracking.
now infor allbetabigcommercemerchants