Zabbix is extremly nice.

Why?

• API Monitoring for Proxmox and Docker/Podman. Aka "you don’t need to setup monitoring for every container/LxC/VM. Do it once for the host,then everything gets autodiscovered.

• Active and passive agents as well as SNMP, IPMI,etc. can be combined as you like. Also does Website/service/application/database monitoring, SSG/Telnet checks and nowadys can even do Prometheus and MQTT/Modbus

• The proxy is really really worth it. It collects data from nodes you do not want exposed and relays them to the server. This includes all kind of inputs and is really easy to setup.

• Due to it being around for two decades there are a shitton of templares for devices - and it’s fairly easy to do your own.

• Unlike other systems (cough checkmk cough Grafana) there are no features that are only available to paying customers.

The most major downsides are the fact that it’s moderately to fairly ressource intensive to run in a small setup(but does consume less than others in large Setups) and it’s far less flashy dashboards. (Which are still powerful,though)