Not sure what's an alternative for Grafana in the open source world in terms of building dashboards for o11y? I'm not aware of one and Grafana is used very extensively in my company...
I moved away from Grafana to Axiom and have not looked back
Weather comp + low load comp + PID which means your room temperature works at the precision range supported by your temperature sensor. In my case, within 0.02 Celsius. Saves energy and makes your house more comfortable. Operated via home assistant.
See real time data in Grafana
https://gasboiler.grafana.net/public-dashboards/8d44381aafa9...
Or Emoncms
https://emoncms.org/app/view?name=MyBoilerIdealLogicH24Opent...
Which OpenTherm device would you recommend?
For example?