A simple add-on to let you display due date when new stock will be available and number on order, on the product info page.
You can set the due number and the stock level at which the display is activated in admin.
Date format and box color can also be changed in admin.
This is NOT an inventory control system. It is just a simple way of showing the customer info to give them confidence in the site. It’s better than just stating you have no stock.
Again totally standalone with no core code change. Simply copy all files into relevant sections and go to admin modules /content and install.