The Tesla coil, and latter the
tesla magnifier, were designed by
Nikola Tesla as devices for Global communication. His aim was to produce a 'World Service', unlike
Marconi's vision of using radio as a point to point wireless telegraph system, Tesla saw radio as a way of globally broadcasting a radio signal that could be picked up by anyone anywhere with the right equipment. His failure was due to a lack of funding when Marconi demonstrated his inferior but vastly cheaper radio, based on Tesla's patents and designs (note as of 1947 Tesla holds the patents for radio).
His eventual aims for the Tesla coil were even grander - he desired to use it to transmit electrical power throughout the earth so that electrical machinery could be run anywhere without batteries just by tuning into the right frequency with the right equipment.
He tested this and was able to transmit some 2000 watts 200 miles to power fluorescent tube lights in front of a small audience. Whether or not this would have worked on a global scale was never proven, and whether it could be done safely, without electrical circuits resonating by accident and picking up kilovolts of unwanted power, was a major concern. The important thing is that it looked damn cool when the test station was powered up and producing 140 feet of man made lightning.