louislam/uptime-kuma
Uptime Kuma is an easy-to-use self-hosted monitoring tool supporting HTTP(s), TCP, Ping, DNS, Docker containers, and Steam game servers, with alerts through 90+ notification services such as Telegram, Discord, Slack, and email. It also offers status pages, certificate info, 2FA, and proxy support, and can be deployed via Docker Compose, Docker, or Node.js.
What this means for indie developers：Indie developers can self-host it to monitor their APIs, backends, and game servers and get alerted on downtime instead of paying for a monitoring service.