The crank is one of the oldest methods of converting human power to mechanical power. Since the invention of the electric generator, cranks are also used for small-scale electricity generation.
Cranks are normally hand-operated. It is important to note that operating a crank can rapidly become tiring. For many applications pedal power (which uses the larger leg muscles) may be a better option.
Hand-cranks are still often a good choice for small-scale mechanical grinders (e.g. coffee grinder), millers, rollers (e.g. pasta machine), shellers, and the like.
Some small-scale water pumps are also hand-cranked.