Nikola Tesla patented several different electric generators, most famously the alternating-current electric generator, invented in 1888, and the still-theoretical pyromagneto electric generator in 1891. Modern generators still use the electrical and mechanical principles behind Tesla's original alternating-current electric generators.
While Tesla's patent of the pyromagneto electric generator explains the theoretical principles behind a "free energy" generator that utilizes radiant energy, no one has managed to produce a working model of this type of generator yet. Despite this, many scientists and academicians continue to research and expand upon Tesla's work in the hopes of manufacturing one.
Tesla also invented the "Tesla Coil" in 1891, which revolutionized both electrical engineering and radio communications.