I have a self hosting Pi Zero W running Gentoo. It started as a joke, but I kept it because it's actually occasionally useful for testing new kernel releases.
I found a fun bug with it a couple years ago: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
It is still able to build software faster than it is released. It takes roughly a month to recompile the entire system :D
I self host some CI runners and do kernel work on a Pi writing some software defined radio things.
For the radio stuff I can just take the Pi, frontend, and a battery pack outside to test.
When I finally move to a place with proper fiber internet I'm going to be hosting several side projects on a handful of Pis.