There was a poster on HN a while ago that recommended¹ the Drok USB volume knob because it can be reconfigured to send keystrokes or mouse actions. Just Google for "configure drok usb volume control knob" for instructions. I reconfigured mine to send mouse scroll events for scrolling through documents.
I have one of those, but never used it too much—if the button got pressed while my Mac was asleep, it immediately woke up and kernel panicked. I don’t know if there was something odd about my machine or my particular PowerMate or what?
Anyone have a favorite 'modern controller' for those of us who no longer have a PowerMate?
¹ https://news.ycombinator.com/item?id=31702940