Does anyone have any ideas on how to create third party connect an app to essentially create a "CUSTOMER PORTAL" - 

Main function would be to notify the customer each time their was activity in their file. (Or to provide them with a customer portal link they could visit at any time to look at their activity taking place behind the scenes). 

I know how to use ZAPIER but I am not sure how I would make this work (or if there is a program in place already to achieve similar results)