Optimizely - A/B testing you'll actually use.
Firebase Crashlytics - The most powerful, yet lightest weight crash reporting solution for iOS and Android developers. | Crashlytics
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
Sentry.io - From error tracking to performance monitoring, developers can see what actually matters, solve quicker, and learn continuously about their applications - from the frontend to the backend.
Google Analytics - Improve your website to increase conversions, improve the user experience, and make more money using Google Analytics. Measure, understand and quantify engagement on your site with customized and in-depth reports.
Apptentive - Apptentive’s mobile customer engagement software helps companies listen to, engage with, and retain their customers.