Is any new technology investigating a mechanical (rather than hydraulic or electrical) method of energy storage, the mechanical equivalent of a battery: an upscale variant of the clockwork spring or rubber band- driven toy?

In some parts of the world there are still many traditional mills (wind, water or animal powered) which rotate too slowly to generate electricity yet could slowly but powerfully "wind up" some sort of mechanical spring. If this energy, when not being used to drive a millstone or pump, could be harnessed and stored in a portable cassette-type container it could then be applied to any number of simple machines or tools, from a bicycle to a winch. These "mechanical batteries" could be distributed and "recharged" regularly, in much the same way as propane gas cylinders are. But rather than fuel cells, these cassettes would serve as the whole motor, aplicable to any machine with a simple axel or spindle.

Pardon my naïveté, I'm a printer, not a physicist. Are there any physical laws against this idea? Could it work? I doubt it, otherwise someone would have put it into practice. But perhaps someone is working along those lines right now without seeing its possible application as a clean energy source for poor rural communities.