Mailtrack.io - The best email tracking solution I've found. Free

CamCard - CamCard reads business cards and save instantly to phone Contacts.

ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.

ABBYY Business Card Reader - Scan cards ≡ in a second and manage them everywhere ☁

Bananatag - Find out what happens to your emails after you press send! Add email tracking, attachment tracking, email scheduling and templates to your daily emails.

Propeller CRM - Small business CRM with deep Gmail integration