The problem with the native Contacts app on your iPhone is that you have to keep the addresses, phone numbers, and emails updated on your own. If your friend moves, or gets a new number, it’s up to you to get the information and enter it correctly into your Contacts app. That’s just so old school.
Addappt is a new app that aims to change all that. You invite others to download and enter their own information in the app, and then every time something changes on their end, the entry in your app changes, too. Better still, the app will push the changes to your native Contacts app, something I’ve not seen before in an app of this type.