Death Ray: The most famous of Tesla's so-called lost inventions was his "death ray." In the 1930s, Tesla claimed that he had invented a machine that was capable of firing focused power beams that could destroy anything within 200 miles. He also claimed that his device could create a "power wall" to defend against any incoming objects. Though the machine was never created, that didn't stop Tesla's rivals from trying to steal the design. The final configuration of the death ray has been lost to history (and that's probably a good thing).