FreeNAS (and TrueNAS) keep track of system alerts and can be configured to send those out via email and a few other services such as Slack and InfluxDB. The selection of these services is pretty limited. Especially limiting is the fact that it does not provide a way to call a custom script or a web service endpoint. But we can capture the alerts from the system and get them out in a roundabout way.
Alerta
Zulip is an open source messaging system that has a unique threaded chat model with topics for threads. Alerta is an open source alert management tool that aggregates alerts from various sources and displays them on an easy to use web interface.