Squeeze: The story of the rubber donut
Works just like it's advertised. Hold it and squeeze.
Mine is stashed in the passenger seat in my girlfriends car to so I can relieve my stress from her driving.
Also, nice way to warm up your forearms on the way to the crag/boulders/fight club.
Builds your strength enough to open those hard to twist Smirnoff Ice bottle caps after that tough day keeping your dog from walking underneath falling climbers