Let’s keep it simple. I’m sure most of us are proud of Docker CPU cycles charted in Grafana via Prometheus, but I’m talking about the house as a whole.
My personal favorite is turning out to be Mealie.
I self-host a bunch of things for my personal use, but Mealie definitely takes the cake in terms of benefitting the entire household. I like the meal planner and the ability to hit the supermarket once to get all the necessary groceries for the week (I’ve never been able to achieve this before). I don’t think there is anything in my stack that even compares with the benefits my house gets of out Mealie.
My runner up would have to be any of the self-hosted media players (Plex, Jellyfin, etc.), but we also have Netflix and a bunch of streaming services, so not that impactful. Home Assistant would also be a close runner up, but it only provides great benefits for me, not the rest of the house. I think Immich will be on this list shortly, when it matures a bit more (are we able to import existing photos yet?)
Some kind of photo management and backup system. I never went the Google Photos route and am now very happy with using Synology Photos and doing backups of my entire diigital life with Synology Hyperbackup. Works great even when NOT exposing it to the internet.
And of course Jellyfin for media streaming.