If I'm understanding this request correctly, this already exists. In NXT, in the Expenses tab, select Settings and then User settings. For each user in your system you can select the frequency with which they are notified that a credit card charge or invoice request needs their approval. We have the Daily option selected for Approvals, which emails everyone each day who has something that is awaiting their approval. The email they receive is helpful as it lists each item pending their approval and has a link they can click to bring them right into the approval screen in NXT.