Open-source options
Zabbix: powerful enterprise monitoring. Prometheus + Grafana: the cloud-native monitoring stack. LibreNMS: networking-focused monitoring. OpenNMS: distributed network monitoring.
Commercial options
SolarWinds NPM: a mature network monitoring platform. Datadog: cloud-native observability. PRTG: easy-to-use monitoring. CloudSino DCOS: full-stack monitoring from hardware to application.