Tool With Integrated Cache Monitoring

Answers

You'd hardly find plugin for Caché for any 3d party tool, while SNMP support included in all InterSystems products allows easy integration with most of them (Zabbix, Nagios, etc). It's even possible to write custom MIB to provide additional metrics, we tried it and it really worked.

Nowadays more lightweight approaches are getting popular, such as Grafana based ones mentioned by Evgeny. I'd personally recommend to use enterprise scale tool such as Zabbix if and only if you really need a solution to monitor all parts of your data center infrastructure (servers, OS, LAN, etc) besides DBMS; otherwise it would look like overkill, I'd prefer Grafana based one.