PagerDuty

PagerDuty handles incident response and on-call scheduling. Monitoring tools send alerts to PagerDuty through its Events API or one of more than 750 integrations, and PagerDuty notifies the person who is on call by app, SMS, phone or e-mail, and escalates when nobody responds. The REST API lets you manage services, schedules, escalation policies and incidents from your own software. Free plan for up to 5 users with one on-call schedule and 100 SMS or phone notifications per month; paid plans for larger teams.