I run a asterisk PJSIP VOIP server on my raspberry pi 5 8GB. I had to use the git and build and recompile and manually load all PJSIP modules because for some reason I couldn't even find an asterisk package on apt db for ARM64 for some fucking reason. Also had to containerize it within a docker because the shit couldn't properly compile without interfering with native system binaries. Shit is so fucking goated and can do PSTN via twilio trunking (call numbers outside of the phone server's number base so basically anyone as long as you make the phone numbers parsed in extensions.conf for each country you wanna call XD). Currently works within LAN but I am planning on making it accessible over the internet using my domain and a tunnel for UDP if possible or just a VPN since my router is being a removed with SIP packets rn. I am having trouble with that part but once it's done I can quite literally ditch any phone plan and use it. Twilio hardly even charges shit for voice rates 🤣🤣🤣. You could also self host your domain + email providing service and then connect that to thunderbird for full schizo-level privacy or sum shit. That's what I do to ditch web-email BS

Pihole, homeassistant, a music server using moodeaudio

You could pihole

So I have a smart plug set up on my printer and print server (old HP 4P with separate network print server.

I have NodeRed watching my CUPS queues via HTTP scraping, and if it sees a job in the queue for that printer, it turns on the print server and printer via the smartplug over wifi. I have seen someone link a project that does something similiar.

Some great light lightweight apps for a 4GB Pi:

• Homeassistant
• Fresh RSS
• Paperless NGX
• Syncthing
• PiHole or Adguard home
• Syncthing

PiHole is a pretty light load, as are Home Assistant and Music Assistant. Frigate starts to make some heat, so don't expect to get a full blown video classification / recording system.

BirdNet Pi!

https://github.com/Nachtzuster/BirdNET-Pi

Another vote for PiHole. It keeps your home network cleaner by ignoring the ads.

On my Rpi4B I run syncthing 24/7. It acts as my sync hub. All other machines are connected to it.

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...

Get yourself and adsb antenna and feed flightaware, flightradar24, and adsbexchange. Help track the skies!

Paperless ngx

let it run dwarf fortress from within the terminal, then ssh into it from wherever you are so you can play df from anywhere in the world. i did this at work.

SANE scan server? Paperless ngx also comes to my mind, find it pretty useful.

AdGuard Home (I prefer it to PiHole)

OtterWiki

Wireguard

Forgejo

Tandoor

You could also setup a git repo for your config files. That way you could revert changes, if you break something.

If you don't want do open your pi up to the internet you could take a look at tailscale. I use this script on my laptop and home pc to share files with sshfs while having any other traffic go through mullvad. Set this up on your pi with it as an exit node and you basically have access from anywhere.

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.

Maybe Nextcloud? Jellyfin?

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

PiHole, PiVPN, maybe a reverse proxy like nginx proxy manager to make connecting to your various web management portals you have an easy way to map it to a human readable url

Jellyfin music server. It needs about 1.2 GB of RAM for itself, plus the system.

qbittorrent (docker) 😁😎

Nextcloud is very useful, or a lemmy Fediverse Instance

Another vote for a music server. Gonic/Navidrome is pretty low power and super useful!

Home assistant is another option, but I'll say that if you're serious about home automation you'll quickly outgrow a Pi. It'll run if you only have a handful of devices though.