Walnuts are extraordinarily tough nuts to crack. Here in the ‘States, we used to do it with a lever-based contraption…
…but in France, they simply used a mallet. French product designer Eloi Goulhot recently built on that, adding the principle of a deadblow mallet to design his own version:
This was apparently a self-directed project, but I bet if Goulhot chooses to pursue it, a manufacturer will bite.