The vibrating reed frequency meter which is the lead image in your link is super cool - never thought about a meter using tuned resonators to measure frequency instead of a discrete time-based counter.

higher freq reeds were also used to switch on/off street lights and household low-tariff water heating here in NZ - hearing the switching tones coming through the stereo was part of my childhood.

A local ham friend build a high power tone generator back in the 70's ... sent slow morse across town in the early hours one night by turning on/off all the streetlights in his neighbourhood