Things I've used mine (plural) for at various points in time, in no particular order: Wireguard & ssh entrypoint into my home network. Pi hole. Kodi. Calibre ebook server. Orchestrating turning on/off IP-based lightbulbs or plugs (since I'm too cheap to get a gateway for ZigBee/Threads/$IOT_protocol) - automatically turning on my Christmas lights at sundown daily after querying an API for my local Civil twilight time was good fun. "NAS server" connected to a cheap 5-disk USB JBOD device. Hosting a low-intensity crawler that ran into blanket IP-range black-listing issues when hosted on cloud-providers. Hosting a Gitea/Forgejo server: I no longer star projects on Github - I mirror them locally and keep them synced, storage is really cheap now. Periodical syncing my backups from NAS to cloud. As a digital "tape recorder" for broadcast radio using FM receiver, aux cable, and USB sound card. Twitter Spaces recording for time-shifting conversations I wanted to listen to later; I beat Twitter's "record" feature to the punch! Twitter crawler/archive bot for a niche community.

Wishlist projects: getting alerted when my home loses electric service or internet connectivity, using UPS and LTE modem. "Calendar dashboard" site that displays the household's schedule for the day on a tablet/jailbroken kindle. A lazy-loading reverse-proxy Caddy API server that will keep the connection open while it turns on my workstation in the background if it's off. Archiving tweets using mitmproxy to passively scrape Twitter's API responses while I use the official mobile client.

Basically anything that I wanted to automate and was not demanding on compute would get assigned to a Pi.