So recently I learned, by practical experiment, that Zabbix will run just perfectly on a Raspberry Pi 3 if you're only looking after a small home or office set up. I've been struggling with problems as the home lan grows more complex, so I really really need to keep an eye on it better (look up my job title if you want to know why!)
The local network has an HP Microserver gen8 (modded, natch, with a Xeon E3 in it instead of the stock processor), two pi-zero's, a pi-4 and a pi-3, along with a bunch of home-automation stuff based mainly around Hive, Hue and generic wifi. I have half-a-dozen services running on the HP, Home-assistant and Node-Red on the pi-4 and the zero's are network management, basically dhcp and dns servers running dnsmasq. The pi-3 was running bluetooth location services, but I'm not using these really so figured monitoring would be a better use for it!
Everything's working, but there's loads more to do. Right now it's vanilla zabbix with some endpoint monitoring in place. I won't point you at anything in particular, other than the official documentation, and this great little guide which got me off the ground. I haven't played with Zabbix for a while, but for a free product once you get your head around the workflow it's pretty straightforward.
Right now I know everything in the house, and this site, are running well. Combined with telegram bot (courtesy of their @botfather) for alerting, and Better Uptime for backup, off-network web monitoring, I'm a happy camper - just have to stay away from dashboard-hypnosis ;)