New Relic is an enterprise grade observability solution in a SaaS package.
They offer a uniform approach to dealing with metrics, logs and events - including a basic but working alert management feature.
If more advanced alert management is needed New Relic offers out-of-the-box integrations with tools like PagerDuty, ServiceNow, Jira, VictorOps and many other services.
The service is easy to get started with and has a generous free tier that works very well for testing Butler alerts.
New Relic is a great choice as it handles both reload failure alerts for the Butler tool as well as both server and Sense specific operational metrics (CPU load, available memory, number of currently connected users etc) from Butler SOS.
More info at newrelic.com