Nanoelectromechanical systems utilizing nanometer-scale assemblies are provided that convert thermal energy into another form of energy that can be used to perform useful work at a macroscopic level. These systems may be used to, for example, produce useful quantities of electric or mechanical energy, heat or cool an external substance or propel an object in a controllable direction. In particular, the present invention includes nanometer-scale beams that reduce the velocity of working substance molecules that collide with this nanometer-scale beam by converting some of the kinetic energy of a colliding molecule into kinetic energy of the nanometer-scale beam. In embodiments that operate without a working substance, the thermal vibrations of the beam itself create the necessary beam motion. In some embodiments, an automatic switch is added to realize a regulator such that the nanometer-scale beams only deliver voltages that exceed a particular amount. Various devices including, piezoelectric, electromagnetic and electromotive force generators, are used to convert the kinetic energy of the nanometer-scale beam into electromagnetic, electric or thermal energy. Systems in which the output energy of millions of these devices is efficiently summed together are also disclosed as well as systems that include nanometer-scale transistors.