Uptime Kuma is an easy-to-use self-hosted monitoring tool.

Vigil is an open-source Status Page you can host on your infrastructure, used to monitor all your servers and apps, and visible to your users.

Percy is a visual testing and monitoring tool that focuses on detecting visual changes in web applications

Datadog is a cloud-based monitoring and analytics platform that provides observability and security for cloud-scale applications

Code, test, and deploy synthetic monitoring at scale.

Create automatic monitors for detecting and scanning changes on web pages, evaluate content based on conditions you define and trigger actions such as notifications, sounds, emails etc.