A simple subway arrival time web page for me and a few of my neighbors showing past headways, predicted next trains based on simple regression, and any alerts. The problem this solves is is we live just 2 stops from a terminus station so that the official subway API predictions start just 2-3 minutes out, when a new train leaves that terminus.

And it also runs a Home Assistant instance inside a docker container, and serves as an MQTT broker for my ESP devices. Everything is through a Cloudflare tunnel.

As for maintenance, your AI harness of choice combined with passwordless sudo (and a good backup system in case things go really south) can make upkeep very pleasant.