Update your website to maintenance mode when website is not working or have problem in database.
Login user can change password from the portal account
Clear all cart product by just one click.
Allow user to add order Note/Comment while place the order
Display Payment Receipt and print payment Receipt on User Portal Account
App(module) provide the funcitonality of upload and download the documents for products.
Website product FAQ (frequently asked question) apps allow you to add common question as well as product specific question.