Free energy suppression conspiracy theory

Free energy suppression (or new energy suppression) is a conspiracy theory that technologically viable, pollution-free, no-cost energy sources are being suppressed by government, corporations, or advocacy groups. Devices allegedly suppressed include perpetual motion machines, cold fusion generators, torus-based generators, reverse-engineered extraterrestrial technology, anti-gravity propulsion systems, and other generally unproven, low-cost energy sources.
The alleged suppression (or weakening) is claimed to have occurred since the mid-19th century and allegedly perpetrated by various government agencies, corporate powers, special interest groups, and fraudulent inventors. The special interest groups are usually claimed to be associated with the fossil fuel or nuclear industry, whose business model would be threatened.
Claims of suppression include:
Some notable people who have been claimed to be suppressed, harassed or killed for their research are Stanley Meyer, 
Eugene Mallove, 
Nikola Tesla, 
and John Kanzius. Notable proponents of the conspiracy theory include Gary McKinnon.