Oh wow, I was really surprised when I saw the photo. I have never seen one like this. Where did you find it? I've always enjoyed antiques that were a useful part of everyday life. I think they just ooze history!
I used to work at the Winchester Mystery House in San Jose CA and one of the things that Sarah Winchester invented and pantented was a sink with a washboard molded into the front of it as an integral part of the sink. Two of them are still in place in the house.
I have always liked washboards. They look great displayed in an old-fashioned kitchen and there are so many different types. But I haven't seen one like yours. VERY NICE!!!!