I run a handful of services for my family on old computers sitting on our home network: family photos, file sync and backups, DNS filtering, that sort of thing.
Old hardware that would otherwise be e-waste is more than enough for the job, and there’s nothing to rent or subscribe to. Our photos, files, and data stay in the house instead of on someone else’s servers, everything works fast over the LAN whether or not the internet is up, and it’s a quiet, ongoing way to keep learning how the systems we depend on actually work.