GetNotify - GetNotify is a free email tracking software solution.
WhoReadMe - WhoReadMe is an email tracking solution that provides details on read duration, recipient location, organization name, operating system etc.
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.
ContactMonkey - ContactMonkey tracks email opens and link clicks.
Mailtrack.io - The best email tracking solution I've found. Free
Intelliverse Email Tracker - Intelliverse Email Tracker provides insights to increase the productivity of your emails.