For a small fleet of VMs, hardware servers, databases, applications, web servers...
Prometheus, Zabbix, anything else you'd recommend?
I'm looking for a low maintenance on premises solution that is free and open source..
I'd recommend taking a look at VictoriaMetrics: open source monitoring solution. It doesn't support logs collection, but for metrics is just great.
Disclaimer: I work for VictoriaMetrics.