goalert

GoAlert does the unglamorous core of PagerDuty: on-call schedules, rotations, escalation policies, and alerts that keep calling your phone until someone acknowledges. Target (yes, the retailer) built it for internal use and open sourced the whole thing under Apache 2.0. Every feature is free with no user limits.

Self-hosting is a single Go binary plus Postgres, about as light as this category gets. The dependency that matters is Twilio: SMS and voice notifications go through your Twilio account, so a real deployment carries a small monthly bill for phone numbers and per-message fees. Slack, email, and webhook notifications work without it.

Solo: overkill, you are the escalation policy. Small teams: GoAlert plus your existing Prometheus or Grafana alerting replaces the core of a PagerDuty bill. Teams that want incident timelines, status pages, and alert noise reduction should look at keephq/keep alongside it or keep paying.

The catch: the feature set has stayed deliberately narrow for years. It pages people, and that's it. No incident management, no postmortems, no AI dedupe. That focus is either exactly what you want or a dealbreaker.