SignalFx uses SignalFx
We use SignalFx to monitor all of SignalFx.. that include the entire stack from core services like Cassandra and AWS EC2 up through custom application metrics from SignalFx itself.
Clarabridge CX Social uses Server Density
Used as main Server Monitoring (load averages, system metrics) and App Monitoring (via custom plugins) tool. Both for graphing data as for sending alerts.