InsightCat - Full-stack monitoring platform for your software and hardware. InsightCat is a cloud-based and AI-powered solution to enhance your system health estate through infrastructure monitoring and alerting capabilities.
OpenCensus - Application and Data, Monitoring, and Monitoring Tools
Site24x7 - Site24x7 offers both free & paid website monitoring services. Monitor websites remotely and receive instant email/sms alerts if your website becomes unavailable. View uptime & performance graphs of your website monitors.
Prometheus - An open-source systems monitoring and alerting toolkit.
AlertBot Website Monitoring - #1 in Website Monitoring
Thanos.io - Open source, highly available Prometheus setup with long term storage capabilities.