During my annual Christmas stockup on stocking stuffers, I got this for my workbench.
I stash it with my capo (for holding strings while I work on saddles), my eletronic tuner (for final tuning), a string winder, and a peanut butter jar lid (for tossing tuner screws or bridge pins to keep up with them).
This Wittner Tuning Fork is an A. I decided to go there because I could easily and quickly tune all the strings close enough to get the electronic tuner to register all strings for final tuneup.
I whack it on the carpeted bench top and place it on the bridge near the pins. It resonates just long enough to get the A string tuned. I toss it back into the bench shelf and go after the others. It's really fun. Cost five bucks USD$.