datadoghq.com

Open-source OpenTelemetry observability (traces, logs, and metrics) with AI-agent incident investigation. The free tier includes 1M spans, 5M logs, and 10M metric points per month with 30-day retention, no credit card required. Fully open-source and self-hostable.

Free for first 100,000 requests (Rails only)

Check if a website is blocked in China by the Great Firewall. It identifies DNS pollution by comparing DNS results and ASN information detected by servers in China versus servers in the United States.

60 uptime monitors, 5-minute interval. Email, Slack alerts.

server security (eBPF agent for Linux), uptime monitoring, on-call alerting/status pages in one product. Free tier includes 10 uptime monitors and heartbeats, 5-minute check intervals, 7-day retention.

Cron job and heartbeat monitoring and status pages for scheduled tasks, backups and background jobs, MCP server available. Free tier: 10 checks, 200 ping log entries, email/chat/webhook alerts, no credit card. Open Source support program for qualifying OS projects.

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.

Heartbeat monitoring for cron jobs, plus HTTP uptime and TLS expiry checks, and a Laravel package that creates checks from your scheduler. Free tier with 10 checks, HTTP interval from 5 min, 30 days of history, 50k pings/mo.