For me, it's my diet and workout buddy. It knows my goals, keeps me on track, does meal planning for me, gives me grocery lists, logs what I eat, when I exercise... anything I want so I don't slack off.
I've enhanced Nanoclaw quite a bit. Moved it to Apple containers (shipped with this Skill already). Then I wrote an API for Nanoclaw to use (food log, workouts, etc), then implemented long-term memory using LanceDB (because I was tired of repeating myself!).