Known for a while that a lot of standards existed, but seeing the list still makes me go wow. Then again I am not surprised, there are so many pros and cons to both high and low frequencies. Higher frequencies mean less flicker and less iron, while lower frequencies equal lower transmission losses and more favorable induction motors. All in all 50/60 is just a compromise adjusted for metric standards. FWIW I once calculated the ideal hypothetical frequency at 72Hz. But chances are as solid state advances 50 years from now everything might be headed toward DC.