Magento 2 Extension -> Out Of Stock Last
This FREE extension enables in the Magento 2.1 the feature of list the out of products in the end of every product list.
Installation / Configuration
1 - Copy the extensions files to your root installation and execute the upgrade command in the bash to install the extension.
2 - Clear all Magento caches.
3 - Now you have to enable the store to show out of stock products, for this check this link. After access Stores > Configurations
4 - Access Catalog > Out Of Stock Last, set the "Enabled" option to "Yes".
5 - Clear all Magento caches.
6 - Now the extension is working.