What’s a tiny script or weekend project you built that ended up lasting for years?

A while back, I threw together a tiny script in a couple of hours just to fix a small personal annoyance. No long-term plan, no roadmap. Years later, it’s still running, and I still get occasional emails from strangers using it. Meanwhile, the bigger startup ideas I spent months planning with actual business models ended up going nowhere. It taught me that you really can't guess what will resonate until you just put stuff out there. Have you ever had a tiny weekend build outlive your actual planned projects?