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.
EmailTracker.cc - Free Email Tracker for Gmail. Close More Deals with Comprehensive Email Tracking, Automated Follow-up Reminders, and Detailed Click Insights
GetNotify - GetNotify is a free email tracking software solution.
Unlimited Email Tracker - Track opens and clicks, set reminders and delays in Gmail
Mailtrack.io - The best email tracking solution I've found. Free
EmailTrackerPro - EmailTrackerPro is an email tracking and spam filter solution.