A Wacom tablet, years ago, when I was working in the graphic arts.
Compared to a mouse, the change in my daily ergonomics was astounding, because using a mouse would hurt my entire arm. When I switching to a tablet (using a custom mouse mode), the mouse click was replaced by tapping the tablet which saved my entire career. Although, fast-forward 10 years, now I do full-stack programming, so I don't use it anymore.