Unlimited Email Tracker - Track opens and clicks, set reminders and delays in Gmail
UserTesting.com - Usability testing has never been easier. Get videos of real people speaking their thoughts as they use websites, mobile apps, prototypes and more!
Newsletter Operating System - All-in-one dashboard to launch & grow your newsletter
Instabug - The top apps in the world rely on Instabug for beta testing, user engagement and crash reporting.
Mailtrack.io - The best email tracking solution I've found. Free
Userbrain - Easy, fast, and affordable user testing for websites and prototypes.