BiggerCake - The data tool that Kickstarter deserves
Mailtrack.io - The best email tracking solution I've found. Free
Campaign Monitor Insights - Actionable analytics for email marketing and automation
Unlimited Email Tracker - Track opens and clicks, set reminders and delays in Gmail
Snov.io - More leads. More sales. More revenue.
MailTracker - MailTracker is a mobile email tracking solution.