Apache SkyWalking
Apache APM platform for service topology, distributed tracing, metrics, logs, and cloud-native diagnostics.
Dynatrace
Checkmk Raw
Nagios-descended infrastructure monitoring with auto-discovery, pre-built service checks, and a polished web UI. Raw edition is GPL-2.0.
Coroot
eBPF-based APM for Kubernetes. Zero-instrumentation service maps and SLO dashboards.
Grafana
The de-facto open-source dashboard layer. Plug into Prometheus, Loki, Tempo, InfluxDB — one pane of glass.
Zabbix
Classic agent-based monitoring suite for hosts, networks, and services. Pre-Prometheus old guard, still actively developed.