Probably it doesn't quite count as a gadget, but repurposing my old PC as a home server. Firstly it makes a great mass storage solution making all my media accessible from any device, no matter what architecture it is and what apps it can run. I also self-host Home Assistant, Syncthing, Radicale, Navidrome, Jellyfin and UrBackup. The ten years old 2 core Pentium with 8GB of RAM can do it all, it's much cheaper to run than half a dozen subscription services and I have total control over my data and privacy.