Maybe it's well known but I just came across journalctl-desktop-notification and I find it very useful so I thought I'd mention it. It's basically a bash script that monitors systemd's journal and pops up a notification when there are warnings or errors (or anything else you want to make it catch besides the default config).
What makes it so useful for the selfhoster is that it can monitor the journal on hosts your user has ssh access to with key authentication (set up in 2s with 'ssh-copy-id').
So case in point, this just popped up:
My reverse proxy can't renew certs, that's bad. For some reason netdata didn't catch it, and the service didn't trigger a system email that would have been forwarded to my smtp. Uptime kuma would have caught it when I would have had only a few days to fix it, but this caught it immediately, and I have 52 days to figure it out.
So you install that on your daily driver and you get these notifications on your desktop. They only have packages for Arch and Gentoo but the thing is just a batch script and a systemd unit. So to install anywhere you just download the "source", extract it, cd to it, and run 'sudo cp -r usr etc /' which is exactly what the Arch package does (line 22).
Just a nifty little tool I wanted to share in case others haven't heard of it.