Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Google StackDriver - Stackdriver provides monitoring services for cloud-powered applications.
WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
Devo - Devo delivers real-time operational & business value from analytics on streaming and historical data to operations.
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
Komodor - The Kubernetes native troubleshooting platform