The lathe is the oldest power tool, being known to the ancient Egyptians (albeit in a hand-powered form). Early industrial revolution-era factories had batteries of power tools driven by belts from overhead shafts. The prime power source was a water wheel or (later) a steam engine. The introduction of the electric motor (and electric distribution networks) in the 1880s made possible the self-powered stationary and portable tools we know today. The global market for power tools is $33 billion (in 2016) and estimated to reach $46 billion in 2025.
Currently, an electric motor is the most popular choice to power stationary tools, though in the past they were powered by windmills, water wheels, and steam. Some museums and hobbyists still maintain and operate stationary tools powered by these older power sources. Portable electric tools may be either corded or battery-powered. Compressed air is the customary power source for nailers and paint sprayers. A few tools (called powder-actuated tools) are powered by explosive cartridges. Tools that run on gasoline or gasoline-oil mixes are made for outdoor use; typical examples include most chainsaws and string trimmers. Other tools like blowtorches will burn their fuel externally to generate heat. Compressed air is universally used where there is a possibility of fuel or vapor ignition - such as automotive workshops. Professional level electric tools differ from DIY or 'consumer' tools by being double insulated and not earthed - in fact, they must not be earthed for safety reasons.
A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labor used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air are also commonly used. Other power sources include steam engines, direct burning of fuels and propellants, such as in powder-actuated tools, or even natural power sources such as wind or moving water. Tools directly driven by animal power are not generally considered power tools.