The The Custom Order Status extension for Magento 2 allows creating any number of custom order statuses to improve the order process for both customers and admins. 

Come with a bunch of features such as assign custom statuses to order states, display all custom order statues to the customer account, notify customers when every order status change, use separate email templates per status and store view, easily manage all custom order statuses from the backend, and much more.

Check more details here : https://www.ulmod.com/custom-order-status-for-magento-2.html