G
Grafana visualises metrics from dozens of sources, from Prometheus and PostgreSQL to cloud monitoring APIs, on one dashboard. It is the standard for infrastructure monitoring because alerting, annotations, and templated dashboards work the way operators expect. It is open source and can be self-hosted.
Where it falls short
It visualises data, it does not store it, so you still need a time-series database, and configuration for complex alerting is verbose.