Yep! Stress balls. We use our hands often, so we forget that they too can use a workout. The repeating act of squeezing and releasing the stress ball helps alleviate stress, promotes better concentration, and helps strengthen those forgotten muscles, among other things.
You can even make your own to fit your size hand by filling a balloon with flour, play dough, water beads, or other ingredients that have a “mushy” consistency to your liking.