Knobs on the stove to regulate heat are pretty awesome. The AGA system of heat storage burners isn't bad either, but knobs are ridiculously convenient.
Aluminum foil.
Rotary knife meat slicers.
Crock-Pots (electric slow cookers), and derivative devices (instant pots - electric multimode pressure cookers). The derivatives are overcomplicated, but people use them to great benefit.
Rice cookers. Blah blah, you can on a stove, how stupid you are. They are a technology advancement that largely automated a chore and improved life for billions.