Long story short: I have Essential Tremors of both hands. My blood pressure medicine, a beta blocker, partially controls the amplitude of my tremors. There is a very expensive device, Cala Trio, that helps with tremors of the hand. It does so by applying an electrical stimulation to the Medial and Radial nerve of the wrist, alternating between the two nerves at the frequency of the tremor.
sooooooooo knowing the frequency of my hand tremor allows be to build a similar device from an Arduino plus some other COTS h/w for about 2% of the cost of the original.