Linux

You can run an (emulated) IBM mainframe on it!

Airsonic music server... There are a few quirks getting it all set up properly, but once it works, it just seems to work forever. Samba file sharing server. Also miniDLNA server can make it easy to watch your movie collection on a tv. The airsonic DLNA doesn't seem to be working currently. I also have a few mastodon bots running from a Pi4. Also could run a tor relay node, which would make it so it's less idle. I have a lot of stuff on my Pi4 and it is still mostly idle most of the time. Thats fine though. For me it's not a huge problem, since overall, my goal is to make it use as little power as possible for all those things. I think thats the whole point is to really use the most lightweight computer that can do what you need. If you just need the print server, you could always get a lower power Pi so you can really optimize how much power needs to be used and maybe even do some sort of Wake on LAN setup so it can be sleeping while not in use.

Check out BOINC: https://boinc.berkeley.edu/

Raspberry Pi I'm not sure if it's worth it. But in short you can advance some science with spare CPU hours. Should be possible to limit it so it doesn't heat up and use just a bit of the cycles depending on other load...

I've got Jellyfin running on an odroid, and it's pretty solid.

Not sure if you're the type to need access to your home network while away, but I also use a pi zero as my "login gateway"--I forward just port 22 to it from the WAN, and I have ssh set up to only allow logins with a key. I can set up dynamic port forwarding and tunnel through to my home network, and that pi zero has no other function (so even if I screw something else up on another server, I can still access my network).

I use my Pi 4B as a DVR for movies and OTA television (MythTV).

There are other tools that handle playback better (OSMC/Kodi, etc) but Myth's configuration and handling of recording schedules is incredibly powerful. Conflict management works well and it can record multiple streams off the same tuner so conflicts are reduced in the first place.

As a general thing because I found myself trying to justify my Gear Acquisition Syndrome -- it's a good idea to split services across devices, rather than having some monolithic home server (which is where most people start). That way if one box goes down, it doesn't take down your whole stack.

If you have some machines scattered about doing different things, it might be time to consider logically grouping services and splitting them across that hardware.

mine is my reverse proxy, using the nginx proxy manager docker install method

Skimmed the title. Brain registered words "rpi" and "linux" underneath it. Instant reaction: "Not another app package format please". 😶‍🌫️

I should spend more time reading properly & less time being an old man yelling at tech.

irks me that it’s mostly idling

Well it's a small processor and relatively efficient one at that so... how about going the opposite direction? How about measuring the power draw on idle? With other task? I don't actually know if that architecture handles that but I saw some things on the do https://developer.arm.com/documentation/100095/0002/functional-description/power-management/dynamic-power-management?lang=en

Also what about using a RPi Zero instead?

Joplin notes. A really nice notetaking app you can selfhost. Simple enough but stil verry advanced.