UptimeRobot

Free for first 100,000 requests (Rails only)

Uptime Monitoring free for up to 100,000 events for unlimited projects and unlimited status pages.

Rails APM with request-based pricing: live traces, slow SQL, N+1 detection, and error tracking. Free forever for 50k requests/month, 7-day retention, 1 app, 1 uptime check, and email alerts. No credit card required.

Noncommercial free server monitoring service, alerts and metrics.

Server monitoring, uptime monitoring, DNS & domain monitoring. Monitor 10 server, 10 uptime, and 10 domain for free.

Powerful server monitoring in a unified platform for metrics and logs, with no setup complexity. Free for one server.

Advanced uptime monitoring with support for large projects and teams. Provides HTTP monitoring, Browser based monitoring, DNS monitoring, domain monitoring, status pages and more. The free tier includes 10 HTTP monitors, 1 DNS monitor and one status page.

Powerful Kubernetes monitoring based on Prometheus. Bring your own Prometheus or install the all-in-one bundle. The free tier includes up to 20 Kubernetes nodes. Alerts via Slack, Microsoft Teams, Discord, and more. Integrations with PagerDuty, OpsGenie, VictorOps, DataDog, and many other tools.