Clinton is looking for an app to manage customer interaction. Leo says that's called Customer Relationship Management (CRM). The king of CRM is called SalesForce. Its what everyone really uses, but it may be overkill for a small business. There was another one called ACT from back in the day. But that is long gone.
Gold Mine is a small business CRM that starts with your contact list and then expands it. Another is SUGAR. Monday is an advertiser and it works well for small businesses. ZoHo. Look at Capterra. That's a good place to start.