UptimeRobot - Free Website Uptime Monitoring
Optimizely - A/B testing you'll actually use.
Uptime Kuma - A fancy self-hosted monitoring tool.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
OnlineOrNot - Uptime monitoring for software teams (even teams of one).
Evolv - Evolv is the visual editor for web-based projects that are used to find better ways to connect with customers in order to improve marketing economics.