Molecular machines are tiny biological machines composed of molecules that can move, work, and interact with each other at the nanoscale, providing new ways of controlling and manipulating matter on a microscopic level. They are the smallest machines known, and operate in a similar way to other machines, but on a much smaller scale. They are composed of proteins, enzymes, and other molecules, and can perform various tasks, such as transporting molecules, rearranging molecules, or carrying out chemical reactions.