I am curious on it

Yes..

https://en.m.wikipedia.org/wiki/Hydropower

https://en.m.wikipedia.org/wiki/Hydroelectricity

 

Yes. One effort is hydroelectricity. Gravitational PE of water is converted to rotational KE of a turbine, which makes electricity.

also: https://deciwatt.global/gravitylight bypasses the need for water

I find the advanced rail energy storage system to be a cool idea, but may not be precisely what’s being sought by the OP

https://interestingengineering.com/energy-storage-trains-work-power-gravity

One of the oldest still working machines in the world is powered totally by gravity.

Gravity is so reliable.

And for really esoteric methods ...

Throwing a mass tangentially around a rotating Blacjk Hole, stealing some of the BH's angular momentum through the frame dragging effect, and having the mass come back with much higher kinetic energy.

1 hour ago, iNow said:

I find the advanced rail energy storage system to be a cool idea, but may not be precisely what’s being sought by the OP

https://interestingengineering.com/energy-storage-trains-work-power-gravity

You need an input in one part of the cycle to let gravity do the work in the other part (same as the light I linked to); in hydro power that’s done by the sun.

How about a water wheel, isn't that harnessing gravity to power a motor? If you've got a waterfall and you build a water wheel, you're using gravity to make the wheel move.