When a body is in the ergosphere of a rapidly rotating super-massive object, as space is dragged around it, kinetic energy is given to the body in that space, relative to the space beyond.
In 1969, Roger Penrose postulated that one could let themselves be affected by this phenomenon and escape the ergosphere as one jumps off a fleeting train (note that this is not condoned in any way), thus gaining an extraordinary speed relative to undistorted space. Though the body would have been still relative to the moving ergosphere, in space not affected by dragging, the body would conserve the momentum it had gained in the doughnut-shaped vessel. Consequently, the object would be moving, relative to undistorted space, at an incredible speed without having exerted any force itself. Of course, it would be energetically costly to eloign one's self from any mass worth sapping in this manner, due to their shear mass and resulting gravitational pull. However, it is conceivable to employ some of the acquired kinetic energy to this end.
It should be noted that due to Law of conservation of angular momentum, if this process were to be repeated enough and with massive enough entities, the rotating object may slow to a point where an viable ergosphere no longer exists. It will be some time yet before the madness of humanity exhausts this source of energy as well, nonetheless.