Just a rock?

[ChrisSarahRox]

Was very curious as to how this one came to look as it does. Any help is appreciated. Some of the photos are before and after a good cleaning. 

[Rockwood]

One place that this look is common would be in water which flows down a steep gradient. A mountain stream comes to mind.

[Ludwigia]

Water, weathering, mechanical and chemical erosion can cause any kind of stone over hundreds, thousands and sometimes millions of years to take on at times the most extraordinary shapes. The consistency, hardness/softness of the stone or parts thereof also plays a major role in the outcome. It would help to know where this stone was found in order to perhaps determine under which processes it was eroded.