Cabot - Self-hosted, easily-deployable monitoring and alerts service - like a lightweight PagerDuty

Cabot is a free, open-source, self-hosted infrastructure monitoring platform that provides some of the best features of PagerDuty, Server Density, Pingdom and Nagios without their cost and complexity.

It provides a web interface that allows you to monitor services (e.g. "Stage Redis server", "Production ElasticSearch cluster") and send telephone, sms or hipchat/email alerts to your on-duty team if those services start misbehaving or go down - all without writing a line of code. Best of all, you can use data that you're already pushing to Graphite/statsd to generate alerts, rather than implementing and maintaining a whole new system of data collectors.